But which half of the horse does it urge into action? (3)
I believe the answer is:
gee
'action?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'but which half of the horse does it urge' is the wordplay.
I cannot quite see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found in the answer.
The remaining letters 'ge' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'into' acts as a link.
Can you help me to learn more?
(Other definitions for gee that I've seen before include "provided by substitute for ginger?" , "Golly" , "American exclamation" , "that's something" , "Urge horse - expression of surprise" .)