The most common and most likely answer to this crossword clue is the 6 letter word BITTER
I've seen this crossword clue in Independent
B
I
T
T
E
R
Buddy explains!

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 BITTER mean?
BITTER noun- (usually in the plural bitters) A liquid or powder, made from bitter herbs, used in mixed drinks or as a tonic.
- A type of beer heavily flavored with hops.
- A turn of a cable about the bitts.
- To make bitter.
- Having an acrid taste (usually from a basic substance).
- Harsh, piercing or stinging.
- Hateful or hostile.
- Cynical and resentful.
- (in combination) A hardware system whose architecture is based around units of the specified number of bits (binary digits).