Two poets ate mashed vegetable (5,6)
I believe the answer is:
sweet potato
'vegetable' is the definition.
(sweet potato is a kind of vegetable)
'two poets ate mashed' is the wordplay.
'mashed' indicates anagramming the letters.
'two'+'poets'+'ate'='twopoetsate'
'twopoetsate' with letters rearranged gives 'SWEET-POTATO'.
(Other definitions for sweet potato that I've seen before include "Tropical root vegetable" , "Vegetable akin to yam" , "Edible root of the Americas" , "Slightly sugary root vegetable" , "South American vegetable" .)