At length, might one press you to stay for a meal? (3)
I believe the answer is:
'at length' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'might one press you to stay for a meal?' is the wordplay.
I cannot really understand how this works, but
'one' could be 'o' (I've seen this in other clues) and 'o' is found in the answer.
'a' is present in the answer.
A single letter 'b' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for boa that I've seen before include "Long, thin, feathery scarf" , "Feathered neckwear - snake" , "Large snake provides a neck decoration" , "Wrap" , "native American" .)