WordNet (r) 3.0 (2006):

fall off
    v 1: come off; "This button had fallen off"
    2: fall heavily or suddenly; decline markedly; "The real estate
       market fell off" [syn: slump, fall off, sink]
    3: diminish in size or intensity [syn: fall off, fall away]

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "fall off":
   abate, ablate, apostacize, apostatize, ascend, bank, bate,
   be eaten away, bolt, break away, cant, careen, carry away, cascade,
   cataract, change sides, climb, collapse, come apart, come down,
   come off, come undone, come unstuck, consume, consume away,
   corrode, crack up, crash, crumble, decline, decrease, defect,
   deliquesce, descend, desert, die, die away, diminish, dip,
   dip down, disintegrate, dive, down, drop, drop down, drop off,
   dwindle, ebb, erode, fade, fail, fall, fall away, fall down,
   fall to pieces, fly apart, get loose, give way, go down,
   go downhill, go off, go over, go to pieces, go uphill, grade,
   gravitate, hit a slump, hit rock bottom, hit the skids, incline,
   keel, languish, lapse, lean, lessen, let up, list, lose altitude,
   melt away, parachute, peel off, pitch, plummet, plunge, pounce,
   pour down, precipitate, rain, rake, reach the depths, retreat,
   rise, run down, run low, sag, secede, shelve, shrink, sidle, sink,
   slant, slide, slip, slope, slump, spring apart, start, stoop,
   subside, swag, sway, switch, switch over, swoop, tail off, tilt,
   tip, touch bottom, trend downward, turn cloak, unravel, uprise,
   wane, waste, waste away, wear, wear away