Offered labourer's first hammer (5)
I believe the answer is:
gavel
'hammer' is the definition.
(I know that gavel is a type of mallet)
'offered labourer's first' is the wordplay.
'offered' becomes 'gave' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'labourer's first' becomes 'l' (gst letter of 'labourer').
'gave'+'l'='GAVEL'
Can you help me to learn more?
(Other definitions for gavel that I've seen before include "Mason's hammer" , "An auctioneer's wooden hammer" , "Small mallet" , "equipment for auctioneer" , "Judge's hammer" .)