The most common and most likely answer to this crossword clue is the 5 letter word BELLY
I've seen this crossword clue in The Times
B
E
L
L
Y
Buddy explains!

The straight part
We know that "stomach" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stomach = belly.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 BELLY mean?
BELLY noun- The abdomen, especially a fat one.
- The stomach.
- The womb.
- The lower fuselage of an airplane.
- The part of anything which resembles the human belly in protuberance or in cavity; the innermost part.
- The hollow part of a curved or bent timber, the convex part of which is the back.
- To position one’s belly; to move on one’s belly.
- To swell and become protuberant; to bulge or billow.
- To cause to swell out; to fill.