Wildebeest seen in big numbers (3)
I believe the answer is:
gnu
'wildebeest' is the definition.
(synonyms)
'in big numbers' is the wordplay.
'in' indicates the answer is hidden within the clue.
'GNU' can be found hidden inside 'big numbers'.
'seen' is the link.
(Other definitions for gnu that I've seen before include "Animal" , "Gun for a kind of deer" , "Gun to get antelope" , "hitherto unknown, we hear" , "Large African antelope" .)