Casual worker not working at first (7)
I believe the answer is:
offhand
'casual' is the definition.
('offhand' can be a synonym of 'casual')
'worker not working at first' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker**).
'not working' becomes 'off' (I've seen this before).
'at first' means one lot of letters go next to another.
'hand' after 'off' is 'OFFHAND'.
(Other definitions for offhand that I've seen before include "Dismissive; curt" , "Brusque" , "Without consideration" , "Where fingerprints are taken" , "Ad lib" .)