sure

1 having or showing a mind free from doubt are you absolutely sure that she said she was coming today? Synonyms assured, clear, cocksure, confident, doubtless, implicit, positive, sanguine, certainRelated Words self-assured, self-conceited, self-confident; decisive, resolute, unfaltering, unhesitating, unquestioning, unwaveringNear Antonyms hesitant, indecisive, vacillating, wavering; diffident, unassumingAntonyms doubtful, dubious, uncertain, unsure

2 impossible to avoid or evade the joke's a sure dud if you don't pause in the right places Synonyms certain, ineluctable, ineludible, inescapable, necessary, inevitable, unavoidable, unescapableRelated Words decided, definite, settled; likely, possible, probable; destined, fated, foreordained, predestined, predetermined, preordained; inexorable, relentless, unremitting, unstoppableNear Antonyms preventable (also preventible); doubtful, dubious, questionable, shaky, unclear; undecided, unsettled; undependable, unreliable; improbable, unlikelyAntonyms avoidable, evadable, uncertain, unsure

3 not likely to fail a sure cure for the winter blues—a week in the Bahamas Synonyms can't-miss, certain, fail-safe, infallible, surefire, unfailingRelated Words dependable, reliable; deadly, unerringNear Antonyms doubtful, questionable, uncertainAntonyms fallible

4 worthy of one's trust a sister is a sure friend for life Synonyms calculable, good, reliable, responsible, safe, secure, solid, steady, dependable, tried, tried-and-true, true, trustable, trustworthy, trustyRelated Words constant, devoted, faithful, fast, loyal, staunch (also stanch), steadfast, true-blue; honest, sincere, single-minded; infallible, unerring; bedrock, firm, sound, strong; effective, telling; attested, authenticated, confirmed, proven, valid, validated, verified; blameless, faultless, guiltless, impeccable, inerrant, irreproachable, unimpeachable, unquestionableNear Antonyms disloyal, faithless, false, fickle, inconstant, perfidious, recreant, traitorous, treacherous, unfaithful, untrue; deceitful, dishonest, lying, mendacious, untruthful; debatable, disputable, doubtable, doubtful, dubious, fishy, problematic (also problematical), questionable, shady, shaky, suspect, uncertain, unsound; hazardous, risky; unconfirmed, untriedAntonyms dodgy [chiefly British], uncertain, undependable, unreliable, unsafe, untrustworthy

5 not capable of being challenged or proved wrong no sure evidence that life exists on other planets Synonyms accomplished, certain, inarguable, incontestable, incontrovertible, indisputable, indubitable, irrefragable, positive, irrefutable, unanswerable, unarguable, unchallengeable, undeniable, unquestionableRelated Words unambiguous, unequivocal; absolute, clear, conclusive, decisive, definite, hands-down; uncontested, uncontradicted, undisputed, unquestionedNear Antonyms controversial, debated, disputed; doubtful, dubious, iffy, inconclusive, indecisive, uncertain; ambiguous, equivocal; academic (also academical), hypothetical, speculative, theoretical (also theoretic)Antonyms answerable, arguable, contradictable, controvertible, debatable, disputable, doubtable, moot, negotiable, problematic (also problematical), questionable, refutable