Monkey really having tail clipped by horse-doctor? (6)
I believe the answer is:
vervet
'monkey' is the definition.
(vervet is a kind of monkey)
'really having tail clipped by horse-doctor?' is the wordplay.
'really' becomes 'very' (I've seen this in another clue).
'having tail clipped' means to remove the last letter.
'by' means one lot of letters go next to another.
'horse doctor?' becomes 'vet' (horse doctor is a kind of vet).
'very' with its final letter taken away is 'ver'.
'ver'+'vet'='VERVET'
(Other definitions for vervet that I've seen before include "South African monkey" , "Common African monkey" , "African guenon monkey" .)