Main part of a book taken by travellers (3,7)

I believe the answer is:

sea passage

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'a book taken by travellers' is the definition.
I can't tell whether this defines the answer.

'main part' is the wordplay.
'main' becomes 'sea' (the main is an old name for the sea).
'part' becomes 'passage' (passage is a kind of part).
'sea'+'passage'='SEA PASSAGE'

'of' is the link.

Can you help me to learn more?

(Another definition for sea passage that I've seen is " main journey".)

I've seen this clue in The Guardian and The Globe and Mail.

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