The most common and most likely answer to this crossword clue is the 8 letter word SCHMALTZ
I've seen this crossword clue in Financial Times
S
C
H
M
A
L
T
Z
More clues leading to the result SCHMALTZ
- Whisky smuggled into school with unknown sloppiness
- Sloppiness in school unknown, introduction of mentoring key
- Suzy regularly consuming last of cognac and Scotch whisky in mawkishness
- Topless dance after separation is out of sentimentality
- Too much emotion in school dance has head spinning
- Mike, during school dance, initially lacking sentimentality
- School master key to zero sloppiness
- Display of emotions unknown after Southern church clamps down on liquor
- Forsaking bed, Scotch whisky boozers at heart display sentimentality
- School cereal comes with variable mush
Buddy explains!

The straight part
We know that "m/ush" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case m/ush = schmaltz.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 SCHMALTZ mean?
SCHMALTZ noun- Liquid chicken fat.
- Excessively sentimental art or music.