Has to report missing black horse (7)
I believe the answer is:
mustang
'horse' is the definition.
(I know that mustang is a horse breed)
'has to report missing black' is the wordplay.
'has to' becomes 'must' (I've seen this before).
'report' becomes 'bang' (report can mean a loud noise).
'missing' indicates named letters should be taken away.
'black' becomes 'b' (abbreviation as in pencil classifications).
'bang' with 'b' removed is 'ang'.
'must'+'ang'='MUSTANG'
(Other definitions for mustang that I've seen before include "Small, half-wild horse of the U.S." , "Hardy wild horse of the American western plains" , "Wild or half-wild horse" , "Feral American horse" , "creature" .)