The Collaborative International Dictionary of English v.0.48:

Prop \Prop\, n. [Akin to LG., D., & Dan. prop stopple, stopper,
   cork, Sw. propp, G. pfropf. See Prop, v.]
   That which sustains an incumbent weight; that on which
   anything rests or leans for support; a support; a stay; as, a
   prop for a building. "Two props of virtue." --Shak.
   [1913 Webster] Propaedeutic

The Collaborative International Dictionary of English v.0.48:

Prop \Prop\, n.
   A shell, used as a die. See Props.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Prop \Prop\, v. t. [imp. & p. p. Propped; p. pr. & vb. n.
   Propping.] [Akin to LG. & D. proppen to cram, stuff, thrust
   into, stop, G. pfropfen, Dan. proppe, Sw. proppa; of
   uncertain origin, cf. G. pfropfen to graft, fr. L. propago
   set, layer of a plant, slip, shoot. Cf. 3d. Prop,
   Propagate.]
   To support, or prevent from falling, by placing something
   under or against; as, to prop up a fence or an old building;
   (Fig.) to sustain; to maintain; as, to prop a declining
   state. --Shak.
   [1913 Webster]

         Till the bright mountains prop the incumbent sky.
                                                  --Pope.
   [1913 Webster]

         For being not propp'd by ancestry.       --Shak.
   [1913 Webster]

         I prop myself upon those few supports that are left me.
                                                  --Pope.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prop
    n 1: a support placed beneath or against something to keep it
         from shaking or falling
    2: any movable articles or objects used on the set of a play or
       movie; "before every scene he ran down his checklist of
       props" [syn: property, prop]
    3: a propeller that rotates to push against air [syn: airplane
       propeller, airscrew, prop]
    v 1: support by placing against something solid or rigid; "shore
         and buttress an old building" [syn: prop up, prop,
         shore up, shore]