assurance (n.)

late 14c., "formal or solemn pledge, promise," also "certainty, full confidence," from Old French asseurance "assurance, promise; truce; certainty, safety, security" (11c., Modern French assurance), from asseurer "to reassure, to render sure" (see assure). Meaning "self-confident" is from 1590s. The word had a negative tinge 18c., often suggesting impudence or presumption.