adj. & adv.
adj. 1 having or seeming to have adequate reason for a belief or assertion. 2 (often foll. by of, or that + clause) convinced. 3 (foll. by of) having a certain prospect or confident anticipation or satisfactory knowledge of. 4 reliable or unfailing (there is one sure way to find out). 5 (foll. by to + infin.) certain. 6 undoubtedly true or truthful.
adv. colloq. certainly. as sure as eggs is eggs see EGG(1). as sure as fate quite certain. be sure (in imper. or infin.; foll. by that + clause or to + infin.) take care to; not fail to (be sure to turn the lights out). for sure colloq. without doubt. make sure 1 make or become certain; ensure. 2 (foll. by of) establish the truth or ensure the existence or happening of. sure enough colloq. 1 in fact; certainly. 2 with near certainty (they will come sure enough). sure-fire colloq. certain to succeed. sure-footed never stumbling or making a mistake. sure-footedly in a sure-footed way. sure-footedness being sure-footed. sure thing int. esp. US colloq. certainly. to be sure 1 it is undeniable or admitted. 2 it must be admitted. sureness n.
[ ME f. OF sur sure (earlier sur) f. L securus SECURE ]