Promise to give a hand to (7)
I believe the answer is:
betroth
'a hand to' is the definition.
I can't judge whether this defines the answer.
'promise to' is the wordplay.
'promise' becomes 'bet' (betting is a kind of promising).
'to' becomes 'roth' (I can't justify this - if you can you should give a lot more credence to this answer).
'bet'+'roth'='BETROTH'
'give' acts as a link.
Can you help me to learn more?
(Other definitions for betroth that I've seen before include "Engage to be married" , "Plight" , "Promise to marry" , "contract" , "Promise to match" .)