The Collaborative International Dictionary of English v.0.48:

Rumple \Rum"ple\, v. t. & i. [imp. & p. p. Rumpled p. pr. &
   vb. n. Rumpling.] [Cf. rimple, and D. rimpelen to wrinkle,
   rompelig rough, uneven, G. r["u]mpfen to wrinkle, MHG.
   r["u]mphen, OHG. rimpfan, Gr. "ra`mfos the crooked beak of
   birds of prey, ? to roam.]
   To make uneven; to form into irregular inequalities; to
   wrinkle; to crumple; as, to rumple an apron or a cravat.
   [1913 Webster]

         They would not give a dog's ear of their most rumpled
         and ragged Scotch paper for twenty of your fairest
         assignats.                               --Burke.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rumple \Rum"ple\, n.
   A fold or plait; a wrinkle. --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rumple
    v 1: disturb the smoothness of; "ruffle the surface of the
         water" [syn: ruffle, ruffle up, rumple, mess up]
    2: to gather something into small wrinkles or folds; "She
       puckered her lips" [syn: pucker, rumple, cockle,
       crumple, knit]
    3: become wrinkled or crumpled or creased; "This fabric won't
       wrinkle" [syn: rumple, crumple, wrinkle, crease,
       crinkle]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "rumple":
   agitate, beat, beat up, bristle, churn, churn up, clutter, cocker,
   cockle, convulse, corrugate, corrugation, crankle, crease, crimp,
   crimple, crinkle, crumple, crush, derange, disarrange, disarray,
   discompose, dishevel, dislocate, disorder, disorganize, disquiet,
   disturb, excite, ferment, flurry, fold, fret, furrow, knit, knot,
   litter, mess, mess up, misarrange, muss, muss up, paddle, perturb,
   perturbate, pucker, purse, ridge, rile, rimple, ripple, rivel,
   roil, roughen, ruck, ruckle, ruffle, scatter, screw, scrunch,
   set on edge, shake, shake up, shirr, stir, stir up, swirl, tousle,
   trouble, upset, whip, whip up, whisk, wimple, work up, wrinkle