Source : Webster's Revised Unabridged Dictionary (1913)

Certain \Cer"tain\, a. [F. certain, fr. (assumed) LL. certanus,
   fr. L. certus determined, fixed, certain, orig. p. p. of
   cernere to perceive, decide, determine; akin to Gr. ? to
   decide, separate, and to E. concern, critic, crime, riddle a
   sieve, rinse, v.]
   1. Assured in mind; having no doubts; free from suspicions
      concerning.

            To make her certain of the sad event. --Dryden.

            I myself am certain of you.           --Wyclif.

   2. Determined; resolved; -- used with an infinitive.

            However, I with thee have fixed my lot, Certain to
            undergo like doom.                    --Milton.

   3. Not to be doubted or denied; established as a fact.

            The dream is certain, and the interpretation thereof
            sure.                                 --Dan. ii. 45.

   4. Actually existing; sure to happen; inevitable.

            Virtue that directs our ways Through certain dangers
            to uncertain praise.                  --Dryden.

            Death, as the Psalmist saith, is certain to all.
                                                  --Shak.

   5. Unfailing; infallible.

            I have often wished that I knew as certain a remedy
            for any other distemper.              --Mead.

   6. Fixed or stated; regular; determinate.

            The people go out and gather a certain rate every
            day.                                  --Ex. xvi. 4.

   7. Not specifically named; indeterminate; indefinite; one or
      some; -- sometimes used independenty as a noun, and
      meaning certain persons.

            It came to pass when he was in a certain city.
                                                  --Luke. v. 12.

            About everything he wrote there was a certain
            natural grace und decorum.            --Macaulay.

   {For certain}, assuredly.

   {Of a certain}, certainly.

   Syn: Bound; sure; true; undeniable; unquestionable;
        undoubted; plain; indubitable; indisputable;
        incontrovertible; unhesitating; undoubting; fixed;
        stated.

Certain \Cer"tain\, n.
   1. Certainty. [Obs.] --Gower.

   2. A certain number or quantity. [Obs.] --Chaucer.

Certain \Cer"tain\, adv.
   Certainly. [Obs.] --Milton.

Source : WordNet®

certain
     adj 1: definite but not specified or identified; "set aside a
            certain sum each week"; "to a certain degree";
            "certain breeds do not make good pets"; "certain
            members have not paid their dues"; "a certain popular
            teacher"; "a certain Mrs. Jones" [syn: {certain(a)}]
     2: having or feeling no doubt or uncertainty; confident and
        assured; "felt certain of success"; "was sure (or certain)
        she had seen it"; "was very sure in his beliefs"; "sure of
        her friends" [syn: {certain(p)}, {sure}] [ant: {uncertain},
         {uncertain}]
     3: established beyond doubt or question; definitely known;
        "what is certain is that every effect must have a cause";
        "it is certain that they were on the bus"; "his fate is
        certain"; "the date for the invasion is certain" [syn: {certain(p)}]
        [ant: {uncertain}]
     4: certain to occur; destined or inevitable; "he was certain to
        fail"; "his fate is certain"; "In this life nothing is
        certain but death and taxes"- Benjamin Franklin; "he faced
        certain death"; "sudden but sure regret"; "he is sure to
        win" [syn: {sure}] [ant: {uncertain}]
     5: established irrevocably; "his fate is sealed" [syn: {sealed}]
        [ant: {unsealed}]
     6: capable of being depended on; "a quick and certain remedy";
        "a sure way to distinguish the two"; "wood dust is a sure
        sign of termites" [syn: {sure}]
     7: exercising or taking care great enough to bring assurance;
        "be certain to disconnect the iron when you are through";
        "be sure to lock the doors" [syn: {sure}]