What does cosponsor mean?
A cosponsor is a person, organization, or nation that joins one or more others in formally supporting or underwriting a venture — most often a piece of legislation, but also events, conferences, publications, and international resolutions. The word can also function as a verb meaning to lend such shared support. In legislative settings, especially in the United States Congress, cosponsorship signals broad backing for a bill: lawmakers frequently attach their names as cosponsors to demonstrate constituent support and build momentum, though the original sponsor retains primary ownership of the measure. Outside politics, organizations commonly cosponsor conferences or charitable initiatives, sharing costs and visibility. The register is neutral-to-formal, and the word carries a cooperative connotation, implying partnership rather than sole responsibility. Its prefix "co-", from Latin, marks joint action, making it part of a productive family of terms like coauthor and cochair. For readers of news and policy writing, recognizing who cosponsors what often reveals the political weight behind an initiative.
One who joins with another or others in sponsoring a bill, event, project, or other undertaking.
"The bill attracted more than forty cosponsors before reaching the floor."
Frequently modified by adjectives such as "lead," "original," or "principal" to indicate degree of involvement.
To act as a joint sponsor of something, together with one or more others.
"Two senators cosponsored the legislation last spring."
Standard plural; used chiefly when referring to multiple legislators or organizations attached to the same bill, event, or initiative.
"The resolution's cosponsors spanned both parties."
In the US Senate, a single bill can gather dozens of cosponsors — but only the original sponsor gets top billing.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cosponsor
The word combines the prefix "co-", from Latin "com-" meaning "together," with "sponsor," which derives from the Latin "spondere," meaning to pledge or promise solemnly. "Sponsor" entered English in the early 17th century, originally referring to a godparent who made pledges on a child's behalf at baptism, before extending to anyone who guarantees or backs an undertaking. "Cosponsor" arose later as the need grew to name joint backers of bills and events, becoming especially common in twentieth-century legislative language. It shares its root with related words such as "sponsorship," "response" (from "respondere"), and "espouse."
Related word forms
How cosponsor is actually used
"Cosponsor" is most common in political and legislative contexts (bills, resolutions) but also applies to events, conferences, and reports. It is typically written without a hyphen in American English; "co-sponsor" appears occasionally in British usage. The verb is usually transitive.
Easily confused with cosponsor
A sponsor bears sole responsibility for backing something, while a cosponsor shares that role jointly with others.