co-author
US /ˌkoʊˈɔː.θər/
UK /ˌkoʊˈɔː.θər/

1.
a person who writes a book, article, or other text with another person or people
:
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She was the co-author of the groundbreaking research paper.
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He worked with a co-author on his latest novel.
1.
to write a book, article, or other text with another person or people
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They decided to co-author a book on sustainable living.
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Professor Lee will co-author the next edition of the textbook.