The Collaborative International Dictionary of English v.0.48:

Lac \Lac\ (l[a^]k), Lakh \Lakh\ (l[aum]k), n. [Hind. lak,
   l[=a]kh, l[=a]ksh, Skr. laksha a mark, sign, lakh.]
   One hundred thousand; also, a vaguely great number; as, a lac
   of rupees. [Written also lack.] [East Indies]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lack \Lack\, v. i.
   1. To be wanting; often, impersonally, with of, meaning, to
      be less than, short, not quite, etc.
      [1913 Webster]

            What hour now?
            I think it lacks of twelve.           --Shak.
      [1913 Webster]

            Peradventure there shall lack five of the fifty.
                                                  --Gen. xvii.
                                                  28.
      [1913 Webster]

   2. To be in want.
      [1913 Webster]

            The young lions do lack, and suffer hunger. --Ps.
                                                  xxxiv. 10.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lack \Lack\ (l[a^]k), 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.
      [1913 Webster]

   2. Deficiency; want; need; destitution; failure; as, a lack
      of sufficient food.
      [1913 Webster]

            She swooneth now and now for lakke of blood.
                                                  --Chaucer.
      [1913 Webster]

            Let his lack of years be no impediment. --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lack \Lack\, v. t. [imp. & p. p. Lacked (l[a^]kt); p. pr. &
   vb. n. Lacking.]
   1. To blame; to find fault with. [Obs.]
      [1913 Webster]

            Love them and lakke them not.         --Piers
                                                  Plowman.
      [1913 Webster]

   2. To be without or destitute of; to want; to need.
      [1913 Webster]

            If any of you lack wisdom, let him ask of God.
                                                  --James i. 5.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lack \Lack\, interj. [Cf. Alack.]
   Exclamation of regret or surprise. [Prov. Eng.] --Cowper.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lack
    n 1: 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:
         lack, deficiency, want]
    v 1: be without; "This soup lacks salt"; "There is something
         missing in my jewelry box!" [syn: miss, lack] [ant:
         feature, have]