I could go on horse to make an impression (4)
I believe the answer is:
etch
'make an impression' is the definition.
(to etch is to make an impression in something)
'i could go on horse' is the wordplay.
I cannot quite understand how this works, but
'horse' could be 'h' (abbreviation as in horse power) and 'h' is found in the answer.
The remaining letters 'etc' 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).
'to' is the link.
Can you help me to learn more?
(Other definitions for etch that I've seen before include "Incribe" , "Engrave (glass/metal)" , "Chase" , "Inscribe" , "Cut design onto metal using acid" .)