What does cosign mean?
Cosign is a verb meaning to sign a document alongside another person, most commonly a loan, lease, or mortgage, so that both parties accept joint legal and financial responsibility. A parent who cosigns a child's student loan, for example, promises the lender that the debt will be repaid even if the borrower fails to pay — making the cosigner's own creditworthiness part of the arrangement. The word also carries a figurative sense: to cosign an idea or statement is to endorse it publicly, as when officials 'cosign' a policy by attaching their names to it. Derived from the Latin prefix co- ('together') and signare ('to mark, to sign'), it entered English in the nineteenth century alongside related terms like countersign and cosignatory. Commonly hyphenated as 'co-sign', the word is neutral in register but frequently appears in financial, legal, and journalistic contexts.
verbTo sign a document jointly with another person, especially to accept equal responsibility for a loan, lease, or other obligation; more broadly, to endorse or approve something publicly.
- To sign a financial document (such as a loan or lease) jointly with another party, thereby sharing legal responsibility for the debt or obligation.
- To endorse, approve, or lend one's public support to an idea, statement, or course of action.
"Her father agreed to cosign the loan so she could buy her first car."
"Because she had no credit history, her grandmother offered to cosign the apartment lease."
"Several prominent senators effectively cosigned the proposal by adding their names to the open letter."
That signature on a student loan isn't just ink — when you cosign, your credit score is on the line just as much as the borrower's.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cosign
Cosign combines the Latin-derived prefix co-, meaning 'together' or 'jointly', with the verb sign, from Latin signare, 'to mark or affix a seal'. The same root gives English signature, signify, and related compounds such as countersign and assign. The compound emerged in English during the nineteenth century as formal joint-signing practices became widespread in banking and law, and it remains closely tied to financial guarantors today.
Related word forms
How cosign is actually used
Often written as the hyphenated variant 'co-sign', especially in British English; both spellings are widely accepted. In everyday speech, 'to cosign' almost always refers to the financial sense of guaranteeing a loan or lease, which carries real risk for the signer — lenders can pursue a cosigner for repayment if the primary borrower defaults. The figurative sense of endorsing an idea is common in journalism and political commentary.
Easily confused with cosign
Cosine is a trigonometric function relating angles and sides of a triangle, while cosign means to sign a document jointly with someone else.