Idler may become annoyed (5)
I believe the answer is:
riled
'annoyed' is the definition.
(I know that annoyed can be written as riled)
'idler may become' is the wordplay.
'may become' indicates anagramming the letters.
'idler' is an anagram of 'RILED'.
(Other definitions for riled that I've seen before include "get angry" , "Made angry" , "Vexed" , "Irritated, provoked" , "Annoyed" .)