The most common and most likely answer to this crossword clue is the 7 letter word ITALIAN
I've seen this crossword clue in Independent
I
T
A
L
I
A
N
More clues leading to the result ITALIAN
- Garibaldi, say, secure at island after revolution
- From Sicily, say, I ain’t worried about Mr Capone!
- Romance? It’s “other things” in Latin name
- Trat’s cut alternate handle in news broadcast?
- It expanded what was written by Dante, among others
- National appeal to arrest a revolutionary
- One translating Latin, a Roman, perhaps
- European got in a tailspin
- European institute, political group, Britain’s got out
- Language from computing: the first adopted by Turing?
Buddy explains!
The straight part
We know that "Waiter in a trat, possibly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case waiter in a trat, possibly = italian.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.