The old woman wouldn't hit us (6)
I believe the answer is:
missus
'the old' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'woman wouldn't hit us' is the wordplay.
I cannot really see how this works, but
'woman' could be 'miss' (miss is a kind of woman) and 'miss' is found in the answer.
'us' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for missus that I've seen before include "Wife (informal)" , "Wife (colloquial)" , "The old lady" , "As partner" , "Dutch American" .)