Naturally it can at length be crushing (3)
I believe the answer is:
boa
'crushing' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for boa that I've seen before include "Fluffy scarf of feathers" , "One who puts the squeeze on" , "Large constrictor snake" , "Wrap" , "strangler" .)