Casual but absent worker (7)
I believe the answer is:
offhand
'casual' is the definition.
(synonyms)
'absent worker' is the wordplay.
'absent' becomes 'off' (I've seen this in other clues).
'worker' becomes 'hand' (hand is a kind of worker).
'off'+'hand'='OFFHAND'
'but' is the link.
(Other definitions for offhand that I've seen before include "Nonchalant" , "Cavalier" , "Brusque" , "Casual or curt, like discarded glove?" , "with a careless manner" .)