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A capitonym is a word that changes its meaning (and sometimes pronunciation) when it is capitalized, the capitalization usually applies due to one form being a proper noun or eponym. It is a portmanteau of the word capital with the suffix -onym. A capitonym is a form of homograph and – when the two forms are pronounced differently – also of heteronym. In situations where both words should be capitalized (such as the beginning of a sentence), there will be nothing to distinguish between them except the context in which they are used.
Although some pairs, such as march and March, are completely unrelated, in other cases, such as august and catholic, the capitalized form is a name that is etymologically related to the uncapitalized form. For example, August derives from the name of Imperator Augustus, who named himself after the word augustus, whence English august came. Likewise, both Catholic and catholic derive from a Greek adjective meaning "universal".
Capital letters may be used to differentiate between a set of objects, and a particular example of that object. For instance in Astronomical terminology a distinction may be drawn between a moon, any natural satellite, and the Moon, to be specific the natural satellite of Earth. Likewise, Sun with a capital may be used to emphasise that the sun of Earth is under discussion.
In English 
Philosophical, religious, and political terms 
A particular example of where capitonyms are prominent is in terminology relating to philosophy, religion, and politics. Capitalized words are often used to differentiate a philosophical concept from how the concept is referred to in everyday life, or to demonstrate respect for an entity or institution.
It is common practice to capitalize the pronouns referring to God (He, Him, His, etc.) Many versions of the Bible, such as the NKJV, therefore capitalize pronouns referring to God. In this tradition, possessive pronouns are also capitalized if one is quoting God; "My" and "Mine" are capitalized, which should not be done when a human speaks. The pronouns "You", "Your", and "Yours" are also sometimes capitalized in reference to God.
Words for transcendent ideas in the Platonic sense are often capitalized, especially when used in a religious context. Examples include "Good", "Beauty", "Truth" or "the One".
The word "god" is capitalized to "God" when referring to the single deity of monotheistic religions such as Christianity, Judaism, or Islam. Other distinctions made include church (meaning a building) and Church (meaning an organization or group of people), and the liturgical Mass, versus the physical mass.
As political parties are often named after philosophies, a capital letter is used to differentiate between a supporter of the philosophy, and a supporter of the party, for instance Liberal, a supporter of any Liberal Party, and liberal, a supporter of the philosophy of liberalism. The Liberal Party of Australia and Liberal Party of Canada are not philosophically liberal; thus, in these countries, adherents of liberalism are sometimes said to be "small-l liberals" to differentiate. Similar examples are conservative/Conservative, democrat/Democrat, libertarian/Libertarian, republican/Republican, socialist/Socialist, and a supporter of labour/Labour.
List of capitonyms in English 
|Capitalised word||Lowercase word||Notes|
|Alpine: of or relating to the Alps||alpine: relating to high mountains; living or growing in high mountains; an alpine plant|
|Arabic: of or relating to the Arabic language or Arabic literature||arabic: (gum) arabic, also called gum acacia, a food ingredient|
|Ares: god of war||ares: plural of are, a metric unit of area||Different pronunciations|
|August: the eighth month of the year||august: majestic or venerable||Different pronunciations|
|Boxing (Day): 26 December||boxing: a sport|
|Calorie: a kilogram-calorie (Cal)||calorie: a gram-calorie (cal)||A practice advocated by some, and not widely followed. The use of the terms 'small calorie' and 'large calorie' or 'gram calorie' and 'kilogram calorie' eliminates any potential confusion. Food product labeling, which often uses Calorie in an ambiguous capitalization, generally refers to kilogram-calories. The distinction is obsolete when the SI unit of energy, the joule, is used instead (1 calorie is about 4.2 joules).|
|Cancer: a constellation and astrological sign, or a genus of crab||cancer: a class of diseases|
|Catholic: relating to the Catholic Church (usually the Roman Catholic Church) (adj.); a member of that church (noun)||catholic: free of provincial prejudices or attachments; universal|
|Celt: (/kɛlt/ or /sɛlt/) a person from an ethnic group using a Celtic language||celt: (/sɛlt/) a prehistoric axe|
|Cuban: from Cuba||cuban: relating to cubes, as in cuban prime (rare technical use)|
|Divine: relating to God||divine: to discover by intuition or insight; to locate water, minerals, etc.||In lower case, the word can take either meaning|
|Earth: a planet||earth: the dry land of this planet|
|Gallic: relating to France or to the ancient territory of Gaul||gallic: relating to galls (abnormal plant growths) or gallic acid|
|German: from Germany||german: closely related (mostly obsolete)|
|God: "the supreme or ultimate reality" (Merriam-Webster's Online Dictionary), the specific deity of most monotheistic religions||god: "a being or object believed to have more than natural attributes and powers and to require human worship" (ibidem), a deity in general||The word for God is capitalized when referring to the monotheistic Supreme Being, but lowercased when referring to the gods of ancient mythology|
|Ionic: relating to Ionia or to a style of classical architecture||ionic: relating to (chemical) ions|
|Italic: of, or relating to Italy||italic: pertaining to a sloping typeface or font|
|Job: subject of a book of the Bible||job: a form of employment||Different pronunciations|
|Lent: the period between Ash Wednesday and Easter||lent: past tense and participle of to lend|
|Lesbian: the demonym for Lesbos||lesbian: a female homosexual (noun) or (adjective) pertaining to lesbians or their relationships|
|March: the third month of the year||march: to walk briskly and rhythmically|
|Marine: infantry specialized in naval or amphibious warfare||marine: something produced by the sea|
|Mass: a liturgical function||mass: a physical property of matter|
|May: the fifth month of the year||may: modal verb|
|Mercury: a planet; the messenger god of the Romans||mercury: chemical element number 80 (symbol Hg)|
|Mosaic: pertaining to Moses||mosaic: a kind of decoration|
|Nice: a city in France||nice: pleasant||Different pronunciations|
|Pole: a Polish person||pole: a long thin cylindrical object; various other meanings|
|Polish: // from Poland||polish: // to create a shiny surface by rubbing ; a compound used in that process||Different pronunciations|
|Reading: the county town of Berkshire, England, or any one of 17 populated areas in the United States named after it||reading: gerund or present participle of the verb "to read", meaning to decode text or other signals.||Different pronunciations|
|Scot: a native of Scotland||scot: a payment, charge, assessment, or tax|
|Scotch: from or relating to Scotland, or a form of whisky||scotch: to put an end to (especially rumours)|
|Swede: a person from Sweden||swede: a vegetable (Brassica napobrassica), also known as rutabaga|
|Tangier: a city in Morocco||tangier: comparative of adjective "tangy".||Tangier is pronounced tan-JEER with [dʒ], tangier pronounced TANG-ee-ər with [ŋ]|
|Turkey: a country in the Middle East||turkey: a bird, often raised for food|
|Welsh: from or relating to Wales||welsh: to renege (on an agreement)||The verb welsh (also spelled welch) is of unknown etymology but is often described as deriving from the adjective Welsh and consequently perceived as insulting to people from Wales, although there is no direct evidence of the connection, nor any popular perception that people from Wales do not comply with agreements|
Examples in poems 
The following poems, of unknown origin, are examples of the use of capitonyms:
In August, an august patriarch
Was reading an ad in Reading, Mass.
Long-suffering Job secured a job
To polish piles of Polish brass.
Other languages 
In other languages there are more, or fewer, of these pairs depending on that language's capitalization rules. For example, in German, where all nouns are capitalized, there are many pairs such as Laut (sound) ~ laut (loud) or Morgen (morning) ~ morgen (tomorrow). In contrast, in Italian, as well as Spanish, very few words (except proper names) are capitalized, so there are extremely few, if any, such pairs. (An example is Messa (Mass) ~ messa (feminine past participle of mettere = to put), though the former is sometimes spelled with a lowercase m too.)
The following list includes only "dictionary words". Personal names (Mark/mark), place-names (China/china), company names (Fiat/fiat), names of publications (Time/time) etc. are all excluded as too numerous to list. Adjectives derived from placenames (e.g. Italic/italic) are allowed. Pairs in which one word is simply a secondary meaning of the other – e.g. Masonry (secret society), which is in essence a peculiar use of the word masonry (wall building) – are omitted.
- Shewan, Ed (2003). Applications of Grammar: Principles of Effective Communication. Liberty Press. p. 112. ISBN 1930367287.
- Elwell, Celia (1996). Practical Legal Writing for Legal Assistants. Cengage Learning. p. 71. ISBN 0314061150.
- The Bible translator: Volumes 43-45. United Bible Societies. 1992. p. 226.
- Cabal, Ted (2007). The Apologetics Study Bible. B&H Publishing Group. pp. xix. ISBN 1586404466.
- The Canadian Style: A Guide to Writing and Editing. Dundurn. 1997. p. 77. ISBN 1550022768.
- The Teaching of Christ: A Catholic Catechism for Adults. Our Sunday Visitor Publishing. 2004. p. 8. ISBN 1592760945.
- The Chicago Manual of Style (16th ed.). 2010. 8.93. ISBN 978-0-226-10420-1.
- Charles Richardson (27 May 2010). "How the Liberal Party left Malcolm Fraser behind". Crikey. Retrieved 2010-12-30.
- Freeman (2010). The Common Sense SAT Workbook. AuthorHouse. p. 315. ISBN 1449037992.