Sure  —adj. 1 (often foll. By of or that) convinced. 2 having adequate reason for a belief or assertion. 3 (foll. By of) confident in anticipation or knowledge of. 4 reliable or unfailing. 5 (foll. By to + infin.) Certain. 6 undoubtedly true or truthful. —adv. Colloq. Certainly.  be sure (in imper. Or infin.; foll. By that + clause or to + infin.) Take care to; not fail to. For sure colloq. Certainly. Make sure make or become certain; ensure. Sure enough colloq. In fact; certainly. To be sure admittedly; indeed, certainly.  sureness n. [french from latin securus]