What the diver must have in his hand? (8)
I believe the answer is:
lifeline
'his hand?' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'what the diver must have in' is the wordplay.
I cannot really understand how this works, but
'in' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for lifeline that I've seen before include "Vital safeguard" , "Vital support?" , "Essential means of support" , "rescue operation?" , "Means of escape" .)