Chem.
Cobalt (symbol Co).

With; together; joint or jointly: used with verbs, nouns, adjectives, and adverbs. See the foot of the page for a list of self-explanatory words containing the prefix co-. [<L co-, var. of com- before gn, h, and vowels <cum with]

1. Math. Of the complement: cosine.
2. Astron. Complement of: codeclination. [<L complementum complement]