Herbivore happy enough with tapir missing outside (5)
I believe the answer is:
okapi
'herbivore' is the definition.
'happy enough with tapir missing outside' is the wordplay.
'happy enough' becomes 'ok'.
'with' means one lot of letters go next to another.
'missing outside' indicates the central letters.
The centre of 'tapir' is 'api'.
'ok'+'api'='OKAPI'
(Other definitions for okapi that I've seen before include "They're wild in central Africa" , "Giraffe-related mammal" , "Beast related to giraffe" , "Giraffe-like mammal" , "Ruminant mammal of Africa" .)