Brooded over point of 9 (7)

'9' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?

'brooded over point' is the wordplay.
'brooded' becomes 'sat' (to brood eggs is to sit on them).
'over' means one lot of letters goes inside another.
'point' becomes 'tine' (I've seen this in other clues).
'sat' going around 'tine' is 'SATINET'.

'of' is the link.