in-1 Also il-, im-, and ir-.
This prefix is added to adjectives to give a negative sense (infertile, inarticulate, inexpensive, invariable) and to nouns to indicate a lack of something (inattention, incapacity, insensitivity). Many examples exist, but in- is not a living form, new words instead being created using un-, to which it is closely related in sense. There is no clear rule deciding which should be used: see un- for more information. See also the next entry.
The prefix is spelled il- before stems beginning in l (illegitimate, illiberal), im- before b, m, and p (imbalance, immoral, impossible), and ir- before r (irrational, irregular).