Piece trimmed becomes level (3)
I believe the answer is:
par
'level' is the definition.
(average level on a golf course)
'piece trimmed' is the wordplay.
'piece' becomes 'part' (synonyms).
'trimmed' means to remove the last letter (the final letter is trimmed off).
'part' with its final letter taken off is 'PAR'.
'becomes' is the link.
(Other definitions for par that I've seen before include "Mean" , "Average standard" , "Average or even, as for the course" , "State of equality" , "Expected golf hole score" .)