The Collaborative International Dictionary of English v.0.48:

Ladder \Lad"der\ (l[a^]d"d[~e]r), n. [OE. laddre, AS.
   hl[=ae]der, hl[=ae]dder; akin to OFries. hladder, OHG.
   leitara, G. leiter, and from the root of E. lean, v.
   [root]40. See Lean, v. i., and cf. Climax.]
   1. A frame usually portable, of wood, metal, or rope, for
      ascent and descent, consisting of two side pieces to which
      are fastened cross strips or rounds forming steps.
      [1913 Webster]

            Some the engines play,
            And some, more bold, mount ladders to the fire.
                                                  --Dryden.
      [1913 Webster]

   2. That which resembles a ladder in form or use; hence, that
      by means of which one attains to eminence; as, to climb
      the corporate ladder.
      [1913 Webster +PJC]

            Lowliness is young ambition's ladder. --Shak.
      [1913 Webster]

   Fish ladder. See under Fish.

   Ladder beetle (Zool.), an American leaf beetle (Chrysomela
      scalaris). The elytra are silvery white, striped and
      spotted with green; the under wings are rose-colored. It
      feeds upon the linden tree.

   Ladder handle, an iron rail at the side of a vertical fixed
      ladder, to grasp with the hand in climbing.

   Ladder shell (Zool.), a spiral marine shell of the genus
      Scalaria. See Scalaria.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ladder
    n 1: steps consisting of two parallel members connected by
         rungs; for climbing up or down
    2: ascending stages by which somebody or something can progress;
       "he climbed the career ladder"
    3: a row of unravelled stitches; "she got a run in her stocking"
       [syn: run, ladder, ravel]
    v 1: come unraveled or undone as if by snagging; "Her nylons
         were running" [syn: ladder, run]

Easton's 1897 Bible Dictionary:

Ladder
   occurs only once, in the account of Jacob's vision (Gen. 28:12).