WordNet (r) 3.0 (2006):

fall away
    v 1: get worse; "My grades are slipping" [syn: slip, drop
         off, drop away, fall away]
    2: diminish in size or intensity [syn: fall off, fall away]

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "fall away":
   abate, ablate, apostacize, apostatize, ascend, bank, bate,
   be eaten away, be found wanting, bolt, break away, cant, careen,
   change sides, climb, collapse, come short, consume, consume away,
   corrode, crumble, decline, decrease, defect, deliquesce, descend,
   desert, die, die away, diminish, dip, dive, drop, drop off,
   dwindle, ebb, erode, fade, fail, fall, fall off, fall short,
   go down, go downhill, go off, go over, go uphill, grade,
   hit a slump, hit rock bottom, hit the skids, incline, keel, lack,
   lag, languish, lapse, lean, lessen, let up, list, lose ground,
   melt away, not answer, not hack it, not make it, not make out,
   not measure up, not stretch, not suffice, pitch, plummet, plunge,
   rake, reach the depths, retreat, rise, run down, run low,
   run short, sag, secede, shelve, shrink, sidle, sink, slant, slide,
   slip, slope, slump, stop short, subside, swag, sway, switch,
   switch over, tail off, tilt, tip, touch bottom, turn cloak, uprise,
   wane, want, waste, waste away, wear, wear away