Source : Webster's Revised Unabridged Dictionary (1913)

Lack \Lack\, n. [OE. lak; cf. D. lak slander, laken to blame,
   OHG. lahan, AS. le['a]n.]
   1. Blame; cause of blame; fault; crime; offense. [Obs.]
      --Chaucer.

   2. Deficiency; want; need; destitution; failure; as, a lack
      of sufficient food.

            She swooneth now and now for lakke of blood.
                                                  --Chaucer.

            Let his lack of years be no impediment. --Shak.

Lack \Lack\, v. t. [imp. & p. p. {Lacked}; p. pr. & vb. n.
   {Lacking}.]
   1. To blame; to find fault with. [Obs.]

            Love them and lakke them not.         --Piers
                                                  Plowman.

   2. To be without or destitute of; to want; to need.

            If any of you lack wisdom, let him ask of God.
                                                  --James i. 5.

Lack \Lack\, v. i.
   1. To be wanting; often, impersonally, with of, meaning, to
      be less than, short, not quite, etc.

            What hour now ? I think it lacks of twelve. --Shak.

            Peradventure there shall lack five of the fifty.
                                                  --Gen. xvii.
                                                  28.

   2. To be in want.

            The young lions do lack, and suffer hunger. --Ps.
                                                  xxxiv. 10.

Lack \Lack\, interj. [Cf. {Alack}.]
   Exclamation of regret or surprise. [Prov. Eng.] --Cowper.

Source : WordNet®

lack
     n : the state of needing something that is absent or
         unavailable; "there is a serious lack of insight into the
         problem"; "water is the critical deficiency in desert
         regions"; "for want of a nail the shoe was lost" [syn: {deficiency},
          {want}]
     v : be without; "This soup lacks salt"; "There is something
         missing in my jewellery box!" [syn: {miss}] [ant: {have}]