Large mammal is fine, knocking back beer (5)
I believe the answer is:
okapi
'large mammal' is the definition.
(type of antelope)
'fine knocking back beer' is the wordplay.
'fine' becomes 'ok' (synonyms).
'knocking back' says the letters should be written backwards.
'beer' becomes 'IPA' (India pale ale).
'ipa' written backwards gives 'api'.
'ok'+'api'='OKAPI'
'is' is the link.
(Other definitions for okapi that I've seen before include "Horned ruminant" , "African mammal related to giraffe" , "Hoofed mammal" , "Wild animal" , "Rare mammal" .)