Source : Webster's Revised Unabridged Dictionary (1913)

Security \Se*cu"ri*ty\, n.; pl. {Securities}. [L. securitas: cf.
   F. s['e]curit['e]. See {Secure}, and cf. {Surety}.]
   1. The condition or quality of being secure; secureness.
      Specifically:
      (a) Freedom from apprehension, anxiety, or care;
          confidence of power of safety; hence, assurance;
          certainty.

                His trembling hand had lost the ease, Which
                marks security to please.         --Sir W.
                                                  Scott.
      (b) Hence, carelessness; negligence; heedlessness.

                He means, my lord, that we are too remiss,
                Whilst Bolingbroke, through our security, Grows
                strong and great in substance and in power.
                                                  --Shak.
      (c) Freedom from risk; safety.

                Give up yourself merely to chance and hazard,
                From firm security.               --Shak.

                Some . . . alleged that we should have no
                security for our trade.           --Swift.

   2. That which secures or makes safe; protection; guard;
      defense. Specifically:
      (a) Something given, deposited, or pledged, to make
          certain the fulfillment of an obligation, the
          performance of a contract, the payment of a debt, or
          the like; surety; pledge.

                Those who lent him money lent it on no security
                but his bare word.                --Macaulay.
      (b) One who becomes surety for another, or engages himself
          for the performance of another's obligation.

   3. An evidence of debt or of property, as a bond, a
      certificate of stock, etc.; as, government securities.

   Syn: Protection; defense; guard; shelter; safety; certainty;
        ease; assurance; carelessness; confidence; surety;
        pledge; bail.

Source : WordNet®

security
     n 1: the state of being free from danger or injury; "we support
          the armed services in the name of national security"
          [ant: {insecurity}]
     2: a formal declaration that documents a fact of relevance to
        finance and investment; the holder has a right to receive
        interest or dividends; "he held several valuable
        securities" [syn: {certificate}]
     3: a department responsible for the security of the
        institution's property and workers; "the head of security
        was a former policeman" [syn: {security department}]
     4: measures taken as a precaution against theft or espionage or
        sabotage etc.; "military security has been stepped up
        since the recent uprising" [syn: {security measures}]
     5: defense against financial failure; financial independence;
        "his pension gave him security in his old age"; "insurance
        provided protection against loss of wages due to illness"
        [syn: {protection}]
     6: freedom from anxiety or fear; "the watch dog gave her a
        feeling of security"
     7: an electrical device that sets off an alarm when someone
        tries to break in [syn: {security system}, {security
        measures}]
     8: property that your creditor can claim in case you default on
        your obligation; "bankers are reluctant to lend without
        good security" [syn: {surety}]
     9: a guarantee that an obligation will be met [syn: {surety}]