Student leaves cougar for one old lady (5)
I believe the answer is:
mamma
'old lady' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'student leaves cougar for one' is the wordplay.
'student' becomes 'l'.
'leaves' indicates named letters should be taken away.
'cougar for one' becomes 'mammal' (cougar is a kind of mammal).
'mammal' with 'l' removed is 'MAMMA'.
Can you help me to learn more?
(Another definition for mamma that I've seen is " Child's parent".)