Lure, a bit fishy! (4)
I believe the answer is:
bait
'lure' is the definition.
(synonyms)
'a bit fishy' is the wordplay.
'fishy' indicates anagramming the letters.
'a'+'bit'='abit'
'abit' is an anagram of 'BAIT'.
(Other definitions for bait that I've seen before include "Deliberately annoy or taunt" , "Annoy; enticement" , "Food to lure fish" , "What lures" , "Worms, for example" .)