Accident has old lady keeping rather quiet (6)
I believe the answer is:
mishap
'accident' is the definition.
(mishap is a kind of accident)
'old lady keeping rather quiet' is the wordplay.
I cannot really understand how this works, but
'lady' could be 'misha' and 'misha' is present in the answer.
'quiet' could be 'p' (music symbol for 'piano', ie soft or quiet) and 'p' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'has' is the link.
Can you help me to learn more?
(Other definitions for mishap that I've seen before include "Accident, unlucky happening" , "Stroke of bad luck" , "An accident, piece of bad luck" , "Unfortunate occurrence" , "An accident or unlucky event" .)