Knight with a poem about antelope (5)
I believe the answer is:
nyala
'antelope' is the definition.
(nyala is a kind of antelope)
'knight with a poem about' is the wordplay.
'knight' becomes 'N' (chess abbreviation).
'with' means one lot of letters go next to another.
'poem' becomes 'lay' (lay is a kind of poem).
'about' shows that the letters should be reversed in order.
'a'+'lay'='alay'
'alay' reversed gives 'yala'.
'n'+'yala'='NYALA'
(Other definitions for nyala that I've seen before include "crested antelope" , "Antelope of southern Africa" , "Spiral-horned antelope" , "South African native" , "one of a herd" .)