co-

co-
co- /kəʊ $ koʊ/ prefix1. together with:
    to coexist (=exist together or at the same time)
    coeducation (=with boys and girls together)
2. doing something with someone else as an equal or with less responsibility:
    my co-author (=someone who wrote the book with me)
    the co-pilot (=someone who helps a pilot)