In business, he’ll give a hand (6)
I believe the answer is:
dealer
'in business he'll' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'give a hand' is the wordplay.
'give' becomes 'deal' (dealing is a kind of giving).
'a hand' becomes 'er' (I am not sure about this - if you are sure you should believe this answer much more).
'deal'+'er'='DEALER'
Can you help me to learn more?
(Other definitions for dealer that I've seen before include "See 24" , "Merchant" , "Trader - distributor of cards" , "One gives out the cards" , "Buyer and seller of goods" .)