Use inefficiently or inappropriately (5)
I believe the answer is:
waste
'use inefficiently or inappropriately' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for waste that I've seen before include "Refuse, garbage, rubbish" , "Use inefficiently or inappropriately" , "Fail to use (profitably)" , "''.... not, want not''" , "Atrophy" .)