One sharing a spine with me? (8)

I believe the answer is:

coauthor

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'one sharing a spine with me?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.

This is the entire clue.

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(Other definitions for coauthor that I've seen before include "Collaborator in writing of book" , "Each of two writers of a book" , "Joint writer" .)

I've seen this clue in The Guardian.

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