"voluntary violation of the marriage bed," c.1300, avoutrie, from Old French avouterie (12c.), noun of condition from avoutre, from Latin adulterare "to corrupt" (see adulteration). Modern spelling, with the re-inserted -d-, is from early 15c. (see ad-).In Middle English, also "sex between husband and wife for recreational purposes; idolatry, perversion, heresy." Classified as single adultery (with an unmarried person) and double adultery (with a married person). Old English word was æwbryce "breach of law(ful marriage)" (compare German Ehebruch). Adultery Dune in Arizona corresponds to Navajo sei adilehe "adultery sand," where illicit lovers met privately.