borrowed from Latin com- "with, together with, jointly" also with verbs marking the complete nature of the action, going back to dialectal Indo-European *kom-, whence also Celtic *kom- "together, with" (whence Gaulish com-, con-, nominal prefix [co- before vowel in coetic "and also"], Old Irish com-, con-, verbal and nominal prefix, co [with following nasalization] "with," Welsh cym-, cyf-, cy-, verbal and nominal prefix, Breton kev-, kem-), Germanic *ga- "together, with" (whence Old English ge-, Old High German ga-, ge-, gi-, Old Icelandic g-, Gothic ga-)

NOTE: Latin com- has, in addition to the above variants, the form co- before vowels, h and gn—see co-. G.E. Dunkel (Lexikon der indogermanischen Partikeln und Prominalstämme) regards Indo-European *ko without m as originally a separate particle, to which the adverbial ending *-m has been added. He also treats *kom and *som as distinct particles and hence rejects the reconstruction *ḱom with a palatovelar.