Prince keeping superb racing horse (5)
I believe the answer is:
pacer
'racing horse' is the definition.
'pacer' can be an answer for 'horse' (a horse which paces). I am unsure of the 'racing' bit.
'prince keeping superb' is the wordplay.
'prince' becomes 'pr'.
'keeping' indicates putting letters inside (some letters kept inside).
'superb' becomes 'ace' (ace can informally mean very good).
'pr' enclosing 'ace' is 'PACER'.
Can you help me to learn more?
(Other definitions for pacer that I've seen before include "walker?" , "Racehorse" , "One walking steadily" , "One setting race speed" , "Horse; one setting speed" .)