To write one's name on the back of a check, note, or document; to sign a document to transfer its ownership or to support it officially.
From Middle English endosse, from Old French endosser (to put on the back), from en- (on) + dos (back). Related to 'endorse,' this older spelling reflects the original sense of writing on the back of a document.
Medieval merchants would literally write on the back (dos in French) of documents, which is why 'endoss' and 'endorse' both mean approval—you're putting your name where money was involved!
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