Prefixes (un-, in-, il-, ir-, and dis-) are often used to give adjectives (and some verbs and nouns) a negative meaning. Here are common examples:
like (v) dislike (v)
legal illegal (= against the law)
regular irregular, e.g. irregular verbs
un- is used with many different words, e.g. unfriendly, unable, unemployed (= without a job), untidy (= not in order; in a mess)
im- is used before some words beginning with m or p, e.g. impolite (= rude), impatient (somebody who is impatient wants things to happen now; they cannot wait for things)
il- is used before some words beginning with 1, e.g. illegible
(= cannot be read because the writing is very bad)
ir- is only used before some words beginning with r, e.g. irresponsible
dis- is used before some adjectives, e.g. dishonest, and a few verbs, e.g. dislike, disagree
in- is used before a limited number of words, e.g. invisible (= cannot be seen)
Note: A prefix does not normally change word stress,e.g. happy/unhappy; possible/ impossible. But the stress may change if you want to emphasise the negative or opposite:
- A: Was he happy about the change?
- B: No, he was very unhappy about it.