Eg, pipistrelle (3)
I believe the answer is:
bat
'eg pipistrelle' is the definition.
(pipistrelle is a kind of bat)
This is all the clue.
(Other definitions for bat that I've seen before include "A mammal; a club" , "Cricketer; mammal" , "Night-flyer" , "Small flying mammal - like 11 Across" , "Nocturnal flier" .)