Formidable family keeping a large old female cat (9)

I believe the answer is:

grimalkin

I'm a little stuck... Click here to teach me more about this clue!

'old female cat' is the definition.
'grimalkin' can be an answer for 'cat' (thesaurus). I'm unsure of the 'old female' bit.

'formidable family keeping a large' is the wordplay.
'formidable' becomes 'grim' (I've seen this before).
'family' becomes 'kin' (synonyms).
'keeping' means one lot of letters goes inside another (some letters kept inside).
'large' becomes 'L' (eg in clothes sizes).
'grim'+'kin'='grimkin'
'a'+'l'='al'
'grimkin' going around 'al' is 'GRIMALKIN'.

Can you help me to learn more?

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.