Being sure has to do with being certain, convinced, trustworthy, or dependable. You can trust a sure thing.

Besides being a synonym for yes, sure has to do with lots of kinds of dependability. If you have a sure eye, then you have good aim, maybe with shooting a basketball or throwing darts. If you're sure of yourself, you're confident. A sure thing or sure bet is something almost certain to happen. If you're 100% convinced of something, you're sure of it.

Definitions of sure
  1. adjective
    having or feeling no doubt or uncertainty; confident and assured
    “was very sure in his beliefs”
    sure of her friends”
    synonyms: certain
    confident, convinced, positive
    persuaded of; very sure
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    incertain, uncertain, unsure
    lacking or indicating lack of confidence or assurance
    uncertain or unable to decide about what course to follow
    doubtful, dubious
    fraught with uncertainty or doubt
    acting with uncertainty or hesitance or lack of confidence
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  2. adjective
    certain to occur; destined or inevitable
    “sudden but sure regret”
    “he is sure to win”
    synonyms: certain
    bound, destined
    (usually followed by `to') governed by fate
    doomed, fated
    (usually followed by `to') determined by tragic fate
    foreordained, predestinate, predestined
    established or prearranged unalterably
    in for
    certain to get or have
    capable of being foretold
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    not certain to occur; not inevitable
    chancy, flukey, fluky, iffy
    subject to accident or chance or change
    uncertain because of uncontrollable circumstances
    up in the air
    not yet determined
    not capable of being foretold
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  3. adjective
    impossible to doubt or dispute
    synonyms: indisputable
    established beyond doubt or question; definitely known
  4. adverb
    definitely or positively (`sure' is sometimes used informally for `surely')
    “he'll win sure as shooting”
    “they sure smell good”
    sure he'll come”
    synonyms: certainly, for certain, for sure, sure as shooting, sure enough, surely
  5. adjective
    reliable in operation or effect
    “a sure way to distinguish the two”
    “wood dust is a sure sign of termites”
    synonyms: certain
    dependable, reliable
    worthy of reliance or trust
  6. adjective
    infallible or unfailing
    “a sure (or true) sign of one's commitment”
    consistent with fact or reality; not false
  7. adjective
    certain not to fail
    “a sure hand on the throttle”
    not subject to change or variation especially in behavior
  8. adjective
    (of persons) worthy of trust or confidence
    “a sure (or trusted) friend”
    synonyms: trusted
    trustworthy, trusty
    worthy of trust or belief
  9. adjective
    physically secure or dependable
    “a sure footing”
    “was on sure ground”
    free from danger or risk
  10. adjective
    exercising or taking care great enough to bring assurance
    “be sure to lock the doors”
    synonyms: certain
    exercising caution or showing care or attention
Word Family

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