In haste, Edward rode a horse (5)
I believe the answer is:
steed
'a horse' is the definition.
(steed is a kind of horse)
'in haste edward rode' is the wordplay.
'in' says the answer is hidden in the clue.
'STEED' can be found hidden inside 'haste edward rode'.
(Other definitions for steed that I've seen before include "Swift horse" , "Warhorse" , "(Poetic) horse" , "Trusty horse" , "Literary term for horse" .)