The most common and most likely answer to this crossword clue is the 4 letter word ROMA
I've seen this crossword clue in Independent
R
O
M
A
Buddy explains!
The straight part
We know that "Travellers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case travellers = roma.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 ROMA mean?
ROMA noun- A Romani; a member of the Roma/Romani people.
- A variety of tomato.