The most common and most likely answer to this crossword clue is the 4 letter word SUET
I've seen this crossword clue in The Guardian
S
U
E
T
More clues leading to the result SUET
- Fat woman on top of tram
- Fat, solidified, covering uniform
- Fat American backed 50% of diet
- Girl’s tummy’s beginning to be fat
- Fat students regularly cut down
- What I do to restrict onset of unwanted fat
- Fat solidified across middle of cup
- Tissue-type full of fat?
- She made Adrian M a bit of a pudding
- Fat little girl’s twin with no victory
Buddy explains!

The straight part
We know that "fat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fat = suet.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 SUET mean?
SUET noun- The fatty tissue that surrounds and protects the kidneys; that of sheep and cattle is used in cooking and in making tallow.