Crossword Genius

The last tube? (5)

Ross

I believe the answer is:

straw

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This clue could be a double definition.

'the last' is the first definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'tube?' is the second definition.
(thesaurus)

Can you help me to learn more?

(Other definitions for straw that I've seen before include "Remains of corn" , "Warts (anag.)" , "Stalk of dry grass" , "trifle" , "Stalk - tube for drinking" .)

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