[‘ A word with two opposite or contradictory meanings.']

Pronunciation: Brit. /ˈkɒntrənɪm/,  U.S. /ˈkɑntrəˌnɪm/

Forms:  19– *contranym*,   19– *contronym*. 

Etymology:Formed within English, by derivation. Etymons: contra- prefix, -onym comb. form. <  contra- prefix + -onym comb. form, after antonym n., synonym n., etc.

  A word with two opposite or contradictory meanings.

Contronyms can take the form of polysemous words, e.g. sanction n. (which can mean both ‘a penalty for disobeying a law’ and ‘official permission or approval for an action’), or homographs, e.g. let v.¹ (in the sense ‘to allow’) and let v.² (in the sense ‘to hinder, obstruct’).

1962  J. Herring in /Word Study/ Feb. 8/2 The name contronym (meaning: any word which is used in two senses which seem to contradict each other) is particularly suitable as a label for a word possessing this peculiarity.

1978 /Word Ways/ Feb. 28 Occasionally..two contradictory meanings survive for a single word—the contronyms of Jack Herring.

1992 /Globe & Mail (Toronto)/(Nexis) 10 Oct., /Let/ is one of those Janus words, or contronyms, that have two virtually opposite meanings.

2005  K. Distin /Selfish Meme/ xi. 145 There are even words, known as contronyms, which are their own antonyms.

Examples

• Bound can mean “tied into immobility” or a (or to) “leap or jump”.
• Cleave can mean “to cling” or “to split apart”.
• Clip can mean “attach” or “cut off”.
• Conclude can mean “to start” (a contract) or “to end”.
• 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”.
• Impregnable can mean “invulnerable” or “vulnerable” (to impregnation).
• Let can mean “allow” or “prevent” (A British Passport contains a request that the bearer be allowed to “pass without let or hindrance”).
• Left can mean “remain” or “leave” (“He left the room” or “He was the last one left in the room”).
• Off can mean “activated”, “beginning to make a noise” (e.g. “The alarm went off”) or “deactivated” / “ceasing operation” (e.g. “The alarm turned off by itself”).
• Overlook can mean to miss seeing something, or a place to see something from above.
• Oversight can mean “accidental omission or error”, or “close scrutiny and 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 “entangle”.
• Sanction can mean “approve” or “penalize”.
• Table can mean “to discuss a topic at a meeting” or “to postpone discussion of a topic”.

Resources

• Wikipedia Auto-Antonym https://en.wikipedia.org/wiki/Auto-antonym