All right for a Greek character to have animal (5)
I believe the answer is:
'animal' is the definition.
'all right for a greek character' is the wordplay.
'all right' becomes 'ok' ('ok' can be a synonym of 'all right').
'for' means one lot of letters go next to another.
'greek character' becomes 'pi' (letter from the Greek alphabet).
'to have' acts as a link.
(Other definitions for okapi that I've seen before include "African ruminant" , "Beast related to giraffe" , "creature" , "They're wild in central Africa" , "Rare mammal" .)