The most common and most likely answer to this crossword clue is the 8 letter word POISONED
I've seen this crossword clue in Independent
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Buddy explains!
The straight part
We know that "Embittered" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case embittered = poisoned.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does POISONED mean?
POISONED verb- To use poison to kill or paralyse (somebody).
- To pollute; to cause to become poisonous.
- To cause to become much worse.
- To cause (someone) to hate or to have unfair negative opinions.
- To inhibit the catalytic activity of.
- To place false information into (a cache) as part of an exploit.
- (of a living thing) Killed, paralysed, or harmed by receiving a dose of poison.
- (of food or drink) Containing poison.
- (of a pawn) Such that its capture will lessen the capturing player's chance of winning.