共
キョウ, とも, とも.に, ども

together, both, neither, all, and, alike, with

JLPT3 G4 S6 F174

The relevant oracle bone form of this character is 廾# (pair of hands holding up/out an object in raising it high in offering; compare 具) + an object → serve; offer → *together*; *with*; *share* → *plural/humble suffix*.

[Full Kanji Etymology List]