Wild garlic from butts above square (7)
I believe the answer is:
ramsons
'wild garlic' is the definition.
(synonyms)
'butts above square' is the wordplay.
'butts' becomes 'rams' (ram can mean to butt or smash).
'above' becomes 'on' (above can mean on top of).
'square' becomes 's' (abbreviation).
'rams'+'on'+'s'='RAMSONS'
'from' acts as a link.
(Other definitions for ramsons that I've seen before include "Garlic" , "Relish" .)