ir-

PREFIX

(Usually pronounced [[t]ɪ̱r-[/t]] before an unstressed syllable, and [[t]ɪr-[/t]] before a stressed syllable.)

Ir- is added to words that begin with the letter `r' to form words with the opposite meaning.

His behaviour was becoming increasingly irrational.

...its mixture of satirical wit, irreverence and spontaneity.