Lacking purpose Selma is drunk (7)
I believe the answer is:
aimless
'lacking purpose' is the definition.
(I've seen this in another clue)
'selma is drunk' is the wordplay.
'drunk' indicates an anagram.
'selma'+'is'='selmais'
'selmais' is an anagram of 'AIMLESS'.
(Other definitions for aimless that I've seen before include "Drifting - Melissa (anag)" , "Without direction or ambition" , "not knowing where to go?" , "Rambling" , "With no plan or programme" .)