Bat or viper moved round before noon (7)
I believe the answer is:
vampire
'bat' is the definition.
(vampire bat is a type of bat)
'viper moved round before noon' is the wordplay.
'moved' indicates anagramming the letters.
'round' is an insertion indicator.
'before noon' becomes 'am'.
'viper' is an anagram of 'vpire'.
'vpire' enclosing 'am' is 'VAMPIRE'.
'or' is the link.
(Other definitions for vampire that I've seen before include "Blood sucker" , "Nosferatu, for example" , "It drinks the blood of the living by night" , "Corpse that rises at night to drink the blood of the living" , "Member of the living dead, drinks blood" .)