One of the horses departs after stock’s reduced (5)
I believe the answer is:
equid
'one of the horses' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'departs after stock's reduced' is the wordplay.
'departs' becomes 'd' (abbreviation eg in train timetables).
'after' is a charade indicator (letters next to each other).
'stock's reduced' becomes 'equi' (I can't justify this - if you can you should give a lot more credence to this answer).
'd' put after 'equi' is 'EQUID'.
Can you help me to learn more?
(Other definitions for equid that I've seen before include "could be an ass" , "A mammal of the horse family" , "An ass perhaps" , "A pony, perhaps" .)