In which Jason was nautical (4)

I believe the answer is:

argo

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'in which jason was nautical' is the definition.
The definition suggests a singular noun which matches the answer.

This is the entire clue.

(Other definitions for argo that I've seen before include "Ancient ship" , "Mythological ship" , "Old ship" , "Old boat" , "Jason's boat" .)

I've seen this clue in the Evening Standard.

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