Repel it, horrible snake? (7)
I believe the answer is:
reptile
'snake?' is the definition.
(snake is a kind of reptile)
'repel it horrible' is the wordplay.
'horrible' indicates an anagram.
'repel'+'it'='repelit'
'repelit' with letters rearranged gives 'REPTILE'.
(Other definitions for reptile that I've seen before include "loathsome type" , "Turtle or snake say" , "eg Crocodile" , "Somebody grovelling" , "Cold-blooded animal like lizard or snake" .)