Horse swift as a bird (7)
I believe the answer is:
courser
This might be a double definition.
'horse swift' is the first definition.
'courser' can be an answer for 'horse' (a very fast horse). I am unsure of the 'swift' bit.
'a bird' is the second definition.
(courser is a kind of bird)
'as' is the link.
Can you help me to learn more?
(Other definitions for courser that I've seen before include "Runner" , "Swift horse" , "Hunter of hares - speedy horse or bird" , "One hunting with dogs" .)