The Collaborative International Dictionary of English v.0.48:

Leader \Lead"er\, n.
   1. One who, or that which, leads or conducts; a guide; a
      conductor. Especially:
      (a) One who goes first.
      (b) One having authority to direct; a chief; a commander.
      (c) (Mus.) A performer who leads a band or choir in music;
          also, in an orchestra, the principal violinist; the
          one who plays at the head of the first violins.
      (d) (Naut.) A block of hard wood pierced with suitable
          holes for leading ropes in their proper places.
      (e) (Mach.) The principal wheel in any kind of machinery.
          [Obs. or R.] --G. Francis.
      (f) A horse placed in advance of others; one of the
          forward pair of horses.
          [1913 Webster]

                He forgot to pull in his leaders, and they
                gallop away with him at times.    --Hare.
      (g) A pipe for conducting rain water from a roof to a
          cistern or to the ground; a conductor.
      (h) (Fishing) A net for leading fish into a pound, weir,
          etc.; also, a line of gut, to which the snell of a fly
          hook is attached.
      (i) (Mining) A branch or small vein, not important in
          itself, but indicating the proximity of a better one.
          [1913 Webster]

   2. The first, or the principal, editorial article in a
      newspaper; a leading or main editorial article.
      [1913 Webster]

   3. (Print.)
      (a) A type having a dot or short row of dots upon its
          face.
      (b) pl. a row of dots, periods, or hyphens, used in tables
          of contents, etc., to lead the eye across a space to
          the right word or number.
          [1913 Webster]

   Syn: chief; chieftain; commander. See Chief.
        [1913 Webster]

WordNet (r) 3.0 (2006):

leader
    n 1: a person who rules or guides or inspires others [ant:
         follower]
    2: a featured article of merchandise sold at a loss in order to
       draw customers [syn: drawing card, loss leader, leader]