Endeavour to squeeze butt in (6)
I believe the answer is:
trendy
'in' is the definition.
('in' can mean trendy or fashionable)
'endeavour to squeeze butt' is the wordplay.
'endeavour' becomes 'try' (synonyms).
'to squeeze' is an insertion indicator (inserted letters are squeezed inside).
'butt' becomes 'end' (eg the butt or end of a cigarette).
'try' placed around 'end' is 'TRENDY'.
(Other definitions for trendy that I've seen before include "Voguish" , "following fashion" , "With it, a la mode" , "Fashionable, in style" , "Less sensible; a dye plant" .)