Crossword Genius

On punching good daughter, primate looked amazed (5)

Ross

I believe the answer is:

gaped

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

'daughter primate looked amazed' is the definition.
I can't tell whether this definition defines the answer.

'on punching good' is the wordplay.
'on' is a charade indicator (letters next to each other).
'punching' becomes 'aped' (I can't justify this - if you can you should believe this answer much more).
'good' becomes 'g' (abbreviation).
'aped' after 'g' is 'GAPED'.

Can you help me to learn more?

(Other definitions for gaped that I've seen before include "Was yawning" , "Looked stunned" , "Stared open-mouthed - yawned" , "Opened mouth wide" , "shown astonishment" .)

I've seen this clue in The Independent.
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