Excellent suggestion might finally work (6)
I believe the answer is:
tiptop
'excellent' is the definition.
(I've seen this before)
'suggestion might finally work' is the wordplay.
'suggestion' becomes 'tip' (tip is a kind of suggestion).
'finally' indicates one should take the final letters.
'work' becomes 'op' (abbreviation for opus).
The last letter of 'might' is 't'.
'tip'+'t'+'op'='TIPTOP'
(Other definitions for tiptop that I've seen before include "Jolly good, excellent" , "Very fine" , "Best of its kind" , "First-rate" , "Excellent, super" .)