The most common and most likely answer to this crossword clue is the 7 letter word VEXILLA
V
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L
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A
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The straight part
We know that "Roman/standards" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case roman/standards = vexilla.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 VEXILLA mean?
VEXILLA noun- A flag, banner, or standard.
- A company of troops serving under one standard.
- The sign of the cross.
- The upper petal of a papilionaceous flower.
- The rhachis and web of a feather taken together; the vane.