Lettuce price cut (3)
I believe the answer is:
cos
'lettuce' is the definition.
(cos is a kind of lettuce)
'price cut' is the wordplay.
'price' becomes 'cost' (synonyms).
'cut' means to remove the last letter.
'cost' with its final letter taken off is 'COS'.
(Other definitions for cos that I've seen before include "Salad plant" , "in the Dodecanese?" , "Chief of Staff" , "Casual as" , "Greek island (alternative spelling): Trig abbrev!" .)