Bitter infighting among thirsty vampires? (5,4)

I believe the answer is:

blood feud

I'm a little stuck... Click here to teach me more about this clue!

'bitter' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

I don't understand the rest of the clue.

Can you help me to learn more?

I've seen this clue in The Sun.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.