Ecstasy in club for pound (4)
I believe the answer is:
beat
'pound' is the definition.
(synonyms)
'ecstasy in club' is the wordplay.
'ecstasy' becomes 'E' (informal term for the drug).
'in' indicates putting letters inside.
'club' becomes 'bat' (as in sporting equipment).
'e' inserted into 'bat' is 'BEAT'.
'for' acts as a link.
(Other definitions for beat that I've seen before include "patrol route?" , "Worst round" , "Thrash; pulse" , "Worst - best" , "Tan" .)