The Collaborative International Dictionary of English v.0.48:

Subsidence \Sub*sid"ence\, Subsidency \Sub*sid"en*cy\, n. [L.
   subsidens, -entis, p. pr. of subsidere. See Subside.]
   The act or process of subsiding.
   [1913 Webster]

         The subdual or subsidence of the more violent passions.
                                                  --Bp.
                                                  Warburton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

subsidence
    n 1: an abatement in intensity or degree (as in the
         manifestations of a disease); "his cancer is in remission"
         [syn: remission, remittal, subsidence]
    2: a gradual sinking to a lower level [syn: settling,
       subsiding, subsidence]
    3: the sudden collapse of something into a hollow beneath it
       [syn: cave in, subsidence]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "subsidence":
   avalanche, cadence, catabasis, catenary, cessation, coast,
   collapse, crash, dead set, dead stand, dead stop, deadlock,
   deceleration, declension, decline, decline and fall, decrescendo,
   decurrence, diminuendo, dive, downtrend, downturn, droop, drop,
   dwindling, dying down, ebb, ebbing, fall, full stop, glide,
   glissade, glissando, halt, landslide, landslip, lapse, lock,
   lowering, plunge, remission, retreat, sag, sideslip, sinkage, skid,
   slide, slip, slippage, slither, slowdown, slump, snowslide,
   snowslip, stand, standstill, stillstand, stop, submergence, swag,
   wane, waning