A joining of hands in marriage or work (5)
I believe the answer is:
union
'a joining' is the definition.
(a union joins things)
'of hands in marriage or work' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is present in the answer.
'in' is present in the answer.
The remaining letters 'un' 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 union that I've seen before include "political alliance" , "pearl amongst Shakespeareans" , "Association with a common purpose" , "See 22" , "Alliance of workers" .)