Source : Webster's Revised Unabridged Dictionary (1913)

Fail \Fail\v. i. [imp. & p. p. {Failed}; p. pr. & vb. n.
   {Failing}.] [F. failir, fr. L. fallere, falsum, to deceive,
   akin to E. fall. See {Fail}, and cf. {Fallacy}, {False},
   {Fault}.]
   1. To be wanting; to fall short; to be or become deficient in
      any measure or degree up to total absence; to cease to be
      furnished in the usual or expected manner, or to be
      altogether cut off from supply; to be lacking; as, streams
      fail; crops fail.

            As the waters fail from the sea.      --Job xiv. 11.

            Till Lionel's issue fails, his should not reign.
                                                  --Shak.

   2. To be affected with want; to come short; to lack; to be
      deficient or unprovided; -- used with of.

            If ever they fail of beauty, this failure is not be
            attributed to their size.             --Berke.

   3. To fall away; to become diminished; to decline; to decay;
      to sink.

            When earnestly they seek Such proof, conclude they
            then begin to fail.                   --Milton.

   4. To deteriorate in respect to vigor, activity, resources,
      etc.; to become weaker; as, a sick man fails.

   5. To perish; to die; -- used of a person. [Obs.]

            Had the king in his last sickness failed. --Shak.

   6. To be found wanting with respect to an action or a duty to
      be performed, a result to be secured, etc.; to miss; not
      to fulfill expectation.

            Take heed now that ye fail not to do this. --Ezra
                                                  iv. 22.

            Either my eyesight fails, or thou look'st pale.
                                                  --Shak.

   7. To come short of a result or object aimed at or desired;
      to be baffled or frusrated.

            Our envious foe hath failed.          --Milton.

   8. To err in judgment; to be mistaken.

            Which ofttimes may succeed, so as perhaps Shall
            grieve him, if I fail not.            --Milton.

   9. To become unable to meet one's engagements; especially, to
      be unable to pay one's debts or discharge one's business
      obligation; to become bankrupt or insolvent.

Fail \Fail\, v. t.
   1. To be wanting to; to be insufficient for; to disappoint;
      to desert.

            There shall not fail thee a man on the throne. --1
                                                  Kings ii. 4.

   2. To miss of attaining; to lose. [R.]

            Though that seat of earthly bliss be failed.
                                                  --Milton.

Fail \Fail\, n. [OF. faille, from failir. See {Fail}, v. i.]
   1. Miscarriage; failure; deficiency; fault; -- mostly
      superseded by failure or failing, except in the phrase
      without fail. ``His highness' fail of issue.'' --Shak.

   2. Death; decease. [Obs.] --Shak.

Source : WordNet®

fail
     v 1: fail to do something; leave something undone; "She failed to
          notice that her child was no longer in his crib"; "The
          secretary failed to call the customer and the company
          lost the account" [syn: {neglect}]
     2: be unsuccessful; "Where do today's public schools fail?";
        "The attempt to rescue the hostages failed miserably"
        [syn: {go wrong}, {miscarry}] [ant: {succeed}]
     3: disappoint, prove undependable to; abandon, forsake; "His
        sense of smell failed him this time"; "His strength
        finally failed him"; "His children failed him in the
        crisis" [syn: {betray}]
     4: stop operating or functioning; "The engine finally went";
        "The car died on the road"; "The bus we travelled in broke
        down on the way to town"; "The coffee maker broke"; "The
        engine failed on the way to town"; "her eyesight went
        after the accident" [syn: {go bad}, {give way}, {die}, {give
        out}, {conk out}, {go}, {break}, {break down}]
     5: be unable; "I fail to understand your motives" [ant: {pull
        off}]
     6: judge unacceptable; "The teacher failed six students" [ant:
        {pass}]
     7: fail to get a passing grade; "She studied hard but failed
        nevertheless"; "Did I fail the test?" [syn: {flunk}, {bomb},
         {flush it}] [ant: {pass}]
     8: fall short in what is expected; "She failed in her
        obligations as a good daughter-in-law"; "We must not fail
        his obligation to the victims of the Holocaust"
     9: become bankrupt or insolvent; fail financially and close;
        "The toy company went bankrupt after the competition hired
        cheap Mexican labor"; "A number of banks failed that year"
     10: prove insufficient; "The water supply for the town failed
         after a long drought" [syn: {run out}, {give out}]
     11: get worse; "Her health is declining"