Alright for a Greek character to have animal (5)
I believe the answer is:
'animal' is the definition.
'alright for a greek character' is the wordplay.
'alright' becomes 'ok' ('OK' can be a synonym of 'alright').
'for' means one lot of letters go next to another.
'greek character' becomes 'pi' (letter from the Greek alphabet).
'to have' is the link.
(Other definitions for okapi that I've seen before include "Wild animal" , "browser" , "Small giraffe" , "Ruminant mammal of Africa" , "Native of Central Africa" .)