Open relative culled eastern snake (7)
I believe the answer is:
unclasp
'open' is the definition.
(I've seen this in another clue)
'relative culled eastern snake' is the wordplay.
I cannot really understand how this works, but
'snake' could be 'asp' (asp is a kind of snake) and 'asp' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for unclasp that I've seen before include "let go" , "Loosen grip on" , "Detach (necklace, belt, etc)" , "Unfasten" , "Open - release from grip" .)