Opposites of adjectives in English by adding prefixes

1. What are prefixes?

Prefixes are affixes. We can add prefixes (placed before the stem of the word) to adjectives to form new words.

2. Which prefixes are used to form opposites of adjectives?

The following prefixes are used to form opposites of adjectives: un-, il-, im-, in-, ir-, and non-.

2.1. un-

Adjective Opposite
Sarah is a married woman. Lisa is an unmarried woman.

2.2. il-, im-, in-, ir-

Adjective Opposite
This is a legal activity. That is an illegal activity.
This is a polite boy. That is an impolite boy.
This is a direct object. That is an indirect object.
This is a regular verb. That is an irregular verb.
  • il- goes before the letter l (illegal)
  • im- goes before the letter p (impolite)
  • ir- goes before the letter r (irregular)

2.3. non-

Adjective Opposite
This is a returnable bottle. That is a non-returnable bottle.


In American English the hyphen after non- is normally left out. (nonreturnable)

2.4. Other prefixes

Here are more prefixes that can be used to form opposites.

Adjective Opposite
This is a cyclic graph. That is an acyclic graph.
This is a normal day. That is an abnormal day.
This is social behaviour. That is antisocial behaviour.
This wheel rotates in clockwise direction. That wheel rotates in counterclockwise direction.
This is a coded warning. That is a decoded warning.