The most common and most likely answer to this crossword clue is the 7 letter word VITRIOL
I've seen this crossword clue in The Guardian
V
I
T
R
I
O
L
More clues leading to the result VITRIOL
Buddy explains!
The straight part
We know that "Bitter criticism" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bitter criticism = vitriol.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 VITRIOL mean?
VITRIOL noun- Sulphuric acid and various metal sulphates.
- (by extension) Bitterly abusive language.
- To subject to bitter verbal abuse.
- To dip in dilute sulphuric acid; to pickle.
- To vitriolize.