The kiddies may think him a knockout! (5)
I believe the answer is:
punch
This could be a double definition.
'the kiddies may think him' is the first definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'a knockout' is the second definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?
Can you help me to learn more?
(Other definitions for punch that I've seen before include "Poke" , "Thump" , "Strike with fist" , "Strike, Judy's husband" , "Blow with the fist" .)