He's certainly tasted blood! (7)
I believe the answer is:
vampire
This could be a double definition.
'he's certainly tasted' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'blood' is the second definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for vampire that I've seen before include "A blood-sucker like Dracula" , "fabulous creature" , "eg Dracula" , "Nosferatu, for example" , "Blood sucker" .)