be a co-author on (a book, a paper)
an associate that one works with
a writer who collaborates with others in writing something
writes (books or stories or articles or the like) professionally (for pay)
be the author of
an odorless very poisonous gas that is a product of incomplete combustion of carbon
a hard ferromagnetic silver-white bivalent or trivalent metallic element; a trace element in plant and animal nutrition
