Is it ensure, insure, or assure?
early 15c., "to keep wet; to soak, saturate;" also figuratively "to cause to absorb" (feelings, opinions, etc.), from Latin imbuere "moisten," of uncertain origin, perhaps from the same root as imbrication. Cf. also Old French embu, past participle of emboivre, from Latin imbibere "drink in, soak in" (see imbibe), which might have influenced the English word. Related: Imbued; imbuing.