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c.1400, "a pledge, vow," from Old French promesse "promise, guarantee, assurance" (13c.) and directly from Latin promissum "a promise," noun use of neuter past participle of promittere "send forth; let go; foretell; assure beforehand, promise," from pro- "before" (see pro-) + mittere "to put, send" (see mission). The ground sense is "declaration made about the future, about some act to be done or not done."