The most common and most likely answer to this crossword clue is the 11 letter word BRIDESMAIDS
I've seen this crossword clue in The Guardian
B
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More clues leading to the result BRIDESMAIDS
Buddy explains!
The straight part
We know that "train attendants" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case train attendants = bridesmaids.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 BRIDESMAIDS mean?
BRIDESMAIDS noun- A woman who attends a bride during her wedding ceremony, as part of the main wedding party.
- (entertainment) A person or team that perennially finishes well, but never first.
- To act as a bridesmaid for; to attend a bride during her wedding ceremony.