Horse grabbing Mike's grooming implement (4)
I believe the answer is:
comb
'grooming implement' is the definition.
(tool for grooming oneself)
'horse grabbing mike's' is the wordplay.
'horse' becomes 'cob' (type of horse).
'grabbing' indicates putting letters inside.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'cob' going around 'm' is 'COMB'.
(Other definitions for comb that I've seen before include "Disentangle" , "Fowl's crest" , "Ransack, scour" , "Tidy (hair); some honey" , "Toothed grooming implement" .)