Hopeless - lacking purpose (2,3)
I believe the answer is:
no use
'hopeless' is the definition.
(if something is no use, it is hopeless or futile)
'lacking purpose' is the wordplay.
'lacking' becomes 'no' (eg lacking money means with no money).
'purpose' becomes 'use' (synonyms).
'no'+'use'='NO USE'
(Other definitions for no use that I've seen before include "won't help?" , "Ineffectual" , "Pointless" , "Futile" .)