For a specific purpose (2,3)
I believe the answer is:
ad hoc
'for a specific purpose' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ad hoc that I've seen before include "(Of group) formed for one purpose only" , "For this special purpose (Latin)" , "For a specific purpose, say an arrangement" , "Intended for one specific matter" , "(Of committee) formed for a single purpose" .)