The Collaborative International Dictionary of English v.0.48:

Crumble \Crum"ble\ (kr[u^]m"b'l), v. t. [imp. & p. p. Crumbled
   (kr[u^]m"b'ld); p. pr. & vb. n. Crumbling
   (kr[u^]m"bl[i^]ng).] [Dim. of crumb, v. t., akin to D.
   kruimelen G. kr["u]meln.]
   To break into small pieces; to cause to fall in pieces.
   [1913 Webster]

         He with his bare wand can unthread thy joints,
         And crumble all thy sinews.              --Milton.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

102 Moby Thesaurus words for "crumbling":
   ablation, abrasion, atomization, attrition, beating, breakup,
   brecciation, coming apart, comminution, corrosion, cracking,
   crushing, decadent, decay, declining, decomposition, decrepit,
   degenerate, degradation, deteriorating, detrition, dilapidated,
   dilapidation, disintegrating, disintegration, disjunction,
   disorganization, dissolution, draining, drooping, dusty, dwindling,
   ebbing, effete, erosion, fading, failing, falling, flagging,
   fragmentation, fragmenting, fusty, going to pieces, gone to seed,
   granulation, granulization, grating, grinding, incoherence, infirm,
   languishing, levigation, marcescent, mashing, mildewed, moldering,
   moldy, moss-grown, moth-eaten, musty, pining, poor, poorish,
   pounding, powdering, ravages of time, regressive, resolution,
   retrograde, retrogressive, rotten, rotten at, ruined, ruinous,
   rusty, shredding, shriveling, sinking, sliding, slipping, slumping,
   smashing, stale, subsiding, tabetic, time-scarred, timeworn,
   trituration, unfirm, unsolid, unsound, unstable, unsturdy,
   unsubstantial, waning, wasting, wear, wear and tear, wilting,
   withering, worn, worsening