Six, say, tense before anaesthetic (7,6)

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

'tense before anaesthetic' is the wordplay.
'tense' becomes 'perfect' (perfect tense is a kind of tense).
'before' is a charade indicator (letters next to each other).
'anaesthetic' becomes 'number' (i.e. something that makes things numb).
'perfect'+'number'='PERFECT NUMBER'

'say' is the link.

Can you help me to learn more?