In the end, do your best to contain (6)
I believe the answer is:
trendy
'in' is the definition.
('in' can mean trendy or fashionable)
'end do your best to contain' is the wordplay.
'do your best' becomes 'try'.
'to contain' means one lot of letters goes inside another.
'end' going inside 'try' is 'TRENDY'.
'the' is the link.
(Other definitions for trendy that I've seen before include "Smart" , "Voguish" , "Up to date, fashionable" , "Less sensible; a dye plant" , "'Hip, fashionable (6)'" .)