Terribly slow nocturnal hunters (4)
I believe the answer is:
owls
'nocturnal hunters' is the definition.
(I've seen this in another clue)
'terribly slow' is the wordplay.
'terribly' indicates anagramming the letters.
'slow' anagrammed gives 'OWLS'.
(Other definitions for owls that I've seen before include "Nocturnal bird" , "Avian symbols of wisdom" , "Slow (anag) -- birds of prey" , "Nocturnal birds" , "Members of Parliament" .)