English word cosign comes from English sign, English co-

Detailed word origin of cosign

Dictionary entry	Language	Definition
sign	English (eng)	(North America, uncountable) Physical evidence left by an animal.. (astrology) An astrological sign.. (mathematics) Positive or negative polarity. (Note: it is improper to place a sign on the number zero). (medicine) A property of the body that indicates a disease and, unlike a symptom, is unlikely to be noticed by the patient.. (sometimes, also used uncountably) A visible indication.. [...]
co-	English (eng)	(mathematics) of the opposite, of the counterpart; dual. Partner or subordinate in an activity. To the same degree. Together; mutually; jointly.
cosign	English (eng)	To sign a document jointly with another person, sometimes as an endorsement.

Words with the same origin as cosign