Drifting, your setter’s in a bar (7)
I believe the answer is:
aimless
'drifting' is the definition.
(synonyms)
'your setter's in a bar' is the wordplay.
'your setter's' becomes 'I'm' ('I'm', referring to the setter of the crossword).
'in' indicates putting letters inside.
'bar' becomes 'less' (both can mean 'not including').
'a'+'less'='aless'
'im' put within 'aless' is 'AIMLESS'.
(Other definitions for aimless that I've seen before include "Drifting with no purpose" , "Like characters in 5D {WAITING FOR GODOT]" , "Melissa (anag) -- unmotivated" , "Without purpose or plan" , "Lacking ambition or target" .)