More rum and water, say, for long journey? (7)

I believe the answer is:

odyssey

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'long journey?' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

(Other definitions for odyssey that I've seen before include "Homer's epic poem" , "Gruelling journey as by Homer" , "Epic poem - epic voyage" , "Homerian epic" , "Long, eventful, wandering journey" .)

I've seen this clue in The Guardian.

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