cowriter

From co- +‎ writer.

cowriter (plural cowriters)

1. Someone who writes something together with one or more other people
   • 1988 January 22, Achy Obejas, “Calendar”, in Chicago Reader‎^[1]:

     Joining her will be […] and Catherine MacKinnon, […] cowriter of the controversial and ultimately unconstitutional (if you believe the Seventh District Court of Appeals) Indianapolis antipornography statute.