Ultimately from Latin con-.

This etymology is incomplete. You can help Wiktionary by elaborating on the origins of this term.

From Proto-Celtic *kom- (with, together), from Proto-Indo-European *ḱóm. Cognate with Old Irish com-, Welsh cyf-, Breton kev- or kem-.

As usual in Latin phonology, the sequences ons and onf are pronounced with nasalised long vowels, and the vowel is written with a macron, i.e. cōnspīrō and cōnferō.

Before the letters b or p use the form com-. Sometimes the co- form is used instead.