With it the essay is without purpose (6)
I believe the answer is:
trendy
'with it' is the definition.
(both can mean fashionable)
'essay is without purpose' is the wordplay.
'essay' becomes 'try' (synonyms).
'is without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'purpose' becomes 'end' (both can mean a goal).
'try' placed around 'end' is 'TRENDY'.
'the' is the link.
(Other definitions for trendy that I've seen before include "following latest convention" , "'Hip, fashionable (6)'" , "Stylish" , "Voguish" , "Less sensible; a dye plant" .)