A synonym is a word that means the same as another. Necessary and required are synonyms. An antonym is a word that means the opposite of another. Wet and dry are antonyms. While synonyms and antonyms are not in themselves interesting, the complexities and irregularities of the English language sometimes make synonyms and antonyms interesting to explore. Many complexities result from words having multiple definitions. A trivial example is a word with synonyms that aren't synonyms of each other, the word beam, for example, having the synonyms bar and shine. Similarly, some words have antonyms that are neither synonyms nor antonyms of each other but completely unrelated: the word right, for example, having the antonyms wrong and left.

A more interesting paradox occurs with the word groom, which does not really have an antonym in the strictest sense but has an opposite of sorts in the word bride, which can be used as a prefix to create a synonym, bridegroom.

The word contronym (also antagonym) is used to refer to words that, by some freak of language evolution, are their own antonyms. Both contronym and antagonym are neologisms; however, there is no alternative term that is more established in the English language.

Contronyms are special cases of homographs (two words with the same spelling). Some examples:

anabasis - military advance, military retreat

- military advance, military retreat apology - admission of fault in what you think, say, or do; formal defense of what you think, say, or do

- admission of fault in what you think, say, or do; formal defense of what you think, say, or do aught - all, nothing

- all, nothing bolt - secure, run away

- secure, run away by - multiplication (e.g., a three by five matrix), division (e.g., dividing eight by four)

- multiplication (e.g., a three by five matrix), division (e.g., dividing eight by four) chuffed - pleased, annoyed

- pleased, annoyed cleave - separate, adhere

- separate, adhere clip - fasten, detach

- fasten, detach consult - ask for advice, give advice

- ask for advice, give advice copemate - partner, antagonist

- partner, antagonist custom - usual, special

- usual, special deceptively smart - smarter than one appears, dumber than one appears

- smarter than one appears, dumber than one appears dike - wall, ditch

- wall, ditch discursive - proceeding coherently from topic to topic, moving aimlessly from topic to topic

- proceeding coherently from topic to topic, moving aimlessly from topic to topic dollop - a large amount, a small amount

- a large amount, a small amount dust - add fine particles, remove fine particles

- add fine particles, remove fine particles enjoin - prescribe, prohibit

- prescribe, prohibit fast - quick, unmoving

- quick, unmoving first degree - most severe (e.g., murder), least severe (e.g., burn)

- most severe (e.g., murder), least severe (e.g., burn) fix - restore, castrate

- restore, castrate flog - criticize harshly, promote aggressively

- criticize harshly, promote aggressively garnish - enhance (e.g., food), curtail (e.g., wages)

- enhance (e.g., food), curtail (e.g., wages) give out - produce, stop production

- produce, stop production grade - incline, level

- incline, level handicap - advantage, disadvantage

- advantage, disadvantage help - assist, prevent (e.g., "I can't help it if...")

- assist, prevent (e.g., "I can't help it if...") left - remaining, departed from

- remaining, departed from liege - sovereign lord, loyal subject

- sovereign lord, loyal subject mean - average, excellent (e.g., "plays a mean game")

- average, excellent (e.g., "plays a mean game") off - off, on (e.g., "the alarm went off")

- off, on (e.g., "the alarm went off") out - visible (e.g., stars), invisible (e.g., lights)

- visible (e.g., stars), invisible (e.g., lights) out of - outside, inside (e.g., "work out of one's home")

- outside, inside (e.g., "work out of one's home") oversight - error, care

- error, care pitted - with the pit in, with the pit removed

- with the pit in, with the pit removed put out - extinguish, generate (e.g., something putting out light)

- extinguish, generate (e.g., something putting out light) quiddity - essence, trifling point

- essence, trifling point quite - rather, completely

- rather, completely ravel - tangle, disentangle

- tangle, disentangle rent - buy use of, sell use of

- buy use of, sell use of rinky-dink - insignificant, one who frequents RinkWorks

- insignificant, one who frequents sanction - approve, boycott

- approve, boycott sanguine - hopeful, murderous (obsolete synonym for "sanguinary")

- hopeful, murderous (obsolete synonym for "sanguinary") screen - show, hide

- show, hide seed - add seeds (e.g., "to seed a field"), remove seeds (e.g., "to seed a tomato")

- add seeds (e.g., "to seed a field"), remove seeds (e.g., "to seed a tomato") skinned - with the skin on, with the skin removed

- with the skin on, with the skin removed strike - hit, miss (in baseball)

- hit, miss (in baseball) table - propose (in the United Kingdom), set aside (in the United States)

- propose (in the United Kingdom), set aside (in the United States) transparent - invisible, obvious

- invisible, obvious unbending - rigid, relaxing

- rigid, relaxing variety - one type (e.g., "this variety"), many types (e.g., "a variety")

- one type (e.g., "this variety"), many types (e.g., "a variety") wear - endure through use, decay through use

- endure through use, decay through use weather - withstand, wear away

- withstand, wear away wind up - end, start up (e.g., a watch)

- end, start up (e.g., a watch) with - alongside, against

Finding such idiosyncrasies in slang is much easier. The word bad can be used as slang to mean good. The word bomb has two slang meanings: failure (as usually used in the United States) and success (as usually used in the United Kingdom).

Some noteworthy antonyms aren't homographs (words that are spelled the same) but homophones (words that are pronounced the same). Some of these include:

aural, oral - heard, spoken

- heard, spoken erupt, irrupt - burst out, burst in

- burst out, burst in petalless, petalous - lacking petals, having petals

- lacking petals, having petals raise, raze - erect, tear down

Homophones that are near-antonyms: