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early 13c., "offense, crime, sin," later (late 13c.) "failure, failure to act," from Old French defaute (12c.) "fault, defect, failure, culpability, lack, privation," from Vulgar Latin *defallita "a deficiency or failure," past participle of *defallere, from Latin de- "away" (see de-) + fallere "to deceive, to cheat; to put wrong, to lead astray, cause to be mistaken; to escape notice of, be concealed from" (see fail (v.)). The financial sense is first recorded 1858; the computing sense is from 1966.
late 14c., "be lacking, be missing," also "become weak," from default (n.). Related: Defaulted; defaulting.
Failure to pay a debt when it is due.