Do a puzzle (5)
I believe the answer is:
solve
'do a puzzle' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for solve that I've seen before include "Work out (a clue)" , "Work out (a problem)" , "Find the 3dn to a mystery" , "Figure out the answer" , "Find the key - work out" .)