Not in suitable gear (6)
I believe the answer is:
outfit
'gear' is the definition.
(outfit is a kind of gear)
'not in suitable' is the wordplay.
'not in' becomes 'out' ('out' is the opposite to 'in').
'suitable' becomes 'fit' ('fit' can be similar in meaning to 'suitable').
'out'+'fit'='OUTFIT'
(Other definitions for outfit that I've seen before include "suit" , "Complete set of clothes" , "Business" , "Team" , "Costume" .)