co·write 
(kō-rīt) or co-write
(kō-rīt) or co-writetr.v. co·wrote (-rōt), co·writ·ten (-rĭtn), co·writ·ing, co·writes or co-wrote or co-writ·ten or co-writ·ting or co-writes
To write jointly or in collaboration with another author.
cowrit·er n.