Crossword Genius

It once involved two banks in a row! (6)

Ross

I believe the answer is:

bireme

'it once involved two banks in a row' is the definition.
The definition suggests a singular noun which matches the answer.

This is the entire clue.

(Other definitions for bireme that I've seen before include "ancient craft" , "Old craft with two banks of oars" , "Type of ancient galley" , "Ancient rowed warship" , "Ancient vessel" .)

I've seen this clue in The Times.
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