Casual worker's showing round fellow (7)
I believe the answer is:
offhand
'casual' is the definition.
(synonyms)
'worker's showing round fellow' is the wordplay.
I cannot quite see how this works, but
'round' could be 'hand' (I have seen 'Round of applause ' mean 'hand' so perhaps 'round' could also mean 'hand') and 'hand' is found within the answer.
'fellow' could be 'f' (abbreviation - of a society etc.) and 'f' is present in the answer.
The remaining letters 'of' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for offhand that I've seen before include "Of speech, casual or curt" , "Ungraciously curt" , "Casually thoughtless or inconsiderate" , "Of behaviour, casual or curt" , "Brusque" .)