Is it ensure, insure, or assure?
late 14c., "encourage suppuration;" mid-15c. "bring to maturity," from Latin maturare "to ripen, bring to maturity," from maturus "ripe, timely, early," related to manus "good" and mane "early, of the morning," from PIE root *ma- "good," with derivatives meaning "occurring at a good moment, timely, seasonable, early." Meaning "come or bring to maturity" is from 1620s. The financial sense of "reach the time for payment" is from 1861. Related: Matured; maturing.
mid-15c., "ripe," also "careful, well-considered," from Latin maturus "ripe, timely, early" (see mature (v.)).
mature ma·ture (mə-tyur', -tur', -chur')
Having reached full natural growth or development.
Of, relating to, or characteristic of full mental or physical development.