Contronym

A contronym, contranym or autoantonym is a word with two opposite meanings. For example, the word cleave can mean "to cut apart" or "to bind together". This feature is also called enantiosemy, enantionymy (enantio- means "opposite"), antilogy or autoantonymy. An enantiosemic term is by definition polysemic.

Nomenclature
A contronym is alternatively called an autantonym, auto-antonym, antagonym, enantiodrome, enantionym, Janus word (after the Roman god Janus, who is usually depicted with two faces), self-antonym, antilogy, or addad (Arabic, singular didd).

Linguistic mechanisms
Some pairs of contronyms are true homographs, i.e., distinct words with different etymologies which happen to have the same form. For instance cleave "separate" is from Old English clēofan, while cleave "adhere" is from Old English clifian, which was pronounced differently.

Other contronyms are a form of polysemy, but where a single word acquires different and ultimately opposite definitions. For example, sanction—"permit" or "penalize"; bolt (originally from crossbows)—"leave quickly" or "fix/immobilize"; fast—"moving rapidly" or "fixed in place". Some English examples result from nouns being verbed in the patterns of "add &lt;noun> to" and "remove &lt;noun> from"; e.g. dust, seed, stone. Denotations and connotations can drift or branch over centuries. An apocryphal story relates how Charles II (or sometimes Queen Anne) described St Paul's Cathedral (using contemporaneous English) as "awful, pompous, and artificial", with the meaning (rendered in modern English) of "awe-inspiring, majestic, and ingeniously designed". "Literally" has had a literal meaning of "word for word", but its increasing use as a intensifier in colloquial speech can make it express "not literally but with emphasis". Negative words such as bad and sick sometimes acquire ironic senses by antiphrasis referring to traits that are impressive and admired, if not necessarily positive (that outfit is bad as hell; lyrics full of sick burns).

Some contronyms result from differences in varieties of English. For example, to table a bill means "to put it up for debate" in British English, while it means "to remove it from debate" in American English (where British English would have "shelve", which in this sense has an identical meaning in American English). To barrack, in Australian English, is to loudly demonstrate support, while in British English it is to express disapproval and contempt.

In Latin, sacer has the double meaning "sacred, holy" and "accursed, infamous". Greek δημιουργός gave Latin its demiurgus, from which English got its demiurge, which can refer either to God as the creator or to the devil, depending on philosophical context.

In some languages, a word stem associated with a single event may treat the action of that event as unitary, so in translation it may appear contronymic. For example, Latin hospes can be translated as both "guest" and "host". In some varieties of English, borrow may mean both "borrow" and "lend".

English

 * Cleave can mean "to cling" or "to split apart".
 * Clip can mean "attach" or "cut off".
 * Dust can mean "to remove dust" (cleaning a house) or "to add dust" (e.g., to dust a cake with powdered sugar).
 * Fast can mean "without moving; fixed in place", (holding fast, also as in "steadfast"), or "moving quickly".
 * Obbligato in music traditionally means a passage is "obligatory" but has also been used to mean "optional".
 * Overlook can mean "to make an accidental omission or error" or "to engage in close scrutiny or control".
 * Oversight can mean "accidental omission or error" or "close scrutiny or control".
 * Peruse can mean to "consider with attention and in detail" or "look over or through in a casual or cursory manner".
 * Ravel can mean "to separate" (e.g., threads in cloth) or "to entangle".
 * Sanction can mean "approve" or "penalize".
 * Table can mean "to discuss a topic at a meeting" (British English) or "to postpone discussion of a topic" (American English).

Nouns

 * The Korean noun 앞(ap) may mean either "future" or "past" (distinguished by context).

Verbs

 * The German verb ausleihen, the Dutch verb lenen, the Polish verb pożyczyć, the Russian verb одолжить (odolžítʹ), the Finnish verb lainata, and the Esperanto verb prunti can mean either "to lend" or "to borrow", with case, pronouns, and mention of persons making the sense clear. The verb stem conveys that "a lending-and-borrowing event is occurring", and the other cues convey who is lending to whom. This makes sense because anytime lending is occurring, borrowing is simultaneously occurring; one cannot happen without the other.
 * The German verb umfahren can either mean "to drive around" or "to run over". Both variants are distinguished by stress, though.
 * The Romanian verb a închiria, the French verb louer, the Finnish verb vuokrata and the Spanish alquilar and arrendar mean "to rent" (as the lessee does) as well as "to let" (as the lessor does).
 * The Swahili verb kutoa means both "to remove" and "to add".
 * The Chinese word "大败", it means both "be defeated" and "to defeat".
 * The Persian verb چیدن (čidan) means both "to pluck" and "to arrange" (i.e. by putting objects down).
 * In Spanish (basic meaning "to give"), when applied to lessons or subjects, can mean "to teach", "to take classes" or "to recite", depending on the context. Similarly with the French verb apprendre, which usually means "to learn" but may refer to the action of teaching someone. Dutch  can mean "to teach" or "to learn".
 * The Indonesian verbs menghiraukan and mengacuhkan can mean "to regard" or "to ignore".
 * The Indonesian/Malay adjective usah can mean "required" or "discouraged" (disambiguated by the use of tidak or tak "don't").

Adverbs

 * कल and کل (kal ) may mean either "yesterday" or "tomorrow" (disambiguated by the verb in the sentence).
 * ar ball can mean "a while ago" or "in a little bit/later on"

Agent nouns

 * The Italian, Spanish and French cognates (respectively) ospite, huésped and hôte can mean "host" or "guest". The three words derive from the Latin hospes, which also carries both meanings.

Adjectives

 * The Latin sinister lit. 'left' meant both "auspicious" and "inauspicious", within the respective Roman and Greek traditions of augury. The negative meaning was carried on into French and ultimately English.
 * Latin means "excessive, too much". It maintained this meaning in Spanish, but it was also misinterpreted as "insignificant, without importance".
 * In Vietnamese, means among other things "bright, clear" (from Sino-Vietnamese  明) and "dead, gloomy" (from 冥). Because of this, the name of the dwarf planet Pluto is not adapted from  as in Chinese, Japanese and Korean.
 * Spanish meant originally "blissful, fortunate" as in tierra dichosa, "fortunate land". However it developed an ironic and colloquial meaning "bothersome, unlucky", as in ¡Dichosas moscas!, "Damned flies!".

In translation
Seeming contronyms can arise from translation. In Hawaiian, for example, aloha is translated both as "hello" and as "goodbye", but the essential meaning of the word is "love", whether used as a greeting or farewell. Similarly, 안녕 (annyeong) in Korean can mean both "hello" and "goodbye" but the central meaning is "peace". The Italian greeting ciao is translated as "hello" or "goodbye" depending on the context; the original meaning was "at your service" (literally "(I'm your) slave").