Did Cook sail in one? (6)

I believe the answer is:

galley

I'm a little stuck... Click here to teach me more about this clue!

'sail in one?' is the definition.
'galley' can be an answer for 'sail' (thesaurus). I'm unsure of the 'in one?' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for galley that I've seen before include "Cookhouse on board" , "Kitchen on ship or aircraft" , "Kitchen aboard ship" , "Trireme" , "On-board cooking area" .)

I've seen this clue in the Evening Standard.

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