Old horse with smooth flanks (9)
I believe the answer is:
ironsides
'old horse with smooth flanks' is the definition.
I can't judge whether this definition defines the answer.
'with smooth flanks' is the wordplay.
'with' is a charade indicator (letters next to each other).
'smooth' becomes 'iron' (to smooth down with an iron).
'flanks' becomes 'sides'.
'iron' next to 'sides' is 'IRONSIDES'.
Can you help me to learn more?
(Other definitions for ironsides that I've seen before include "Those having great stamina" , "Oliver Cromwell" , "Cromwell's cavalry" , "Several Edmunds" , "Cromwell's army" .)