Cut price lettuce? (3)
I believe the answer is:
cos
'lettuce?' is the definition.
(cos is a kind of lettuce)
'cut price' is the wordplay.
'cut' means to remove the last letter.
'price' becomes 'cost' (synonyms).
'cost' with its final letter taken away is 'COS'.
(Other definitions for cos that I've seen before include "Senior officers" , "Chief of Staff" , "Greek island (alternative spelling): Trig abbrev!" , "A long-leaved lettuce" , "Island in Mediterranean" .)