WordNet (r) 3.0 (2006):

downturn
    n 1: a worsening of business or economic activity; "the market
         took a downturn" [syn: downturn, downswing]

Moby Thesaurus II by Grady Ward, 1.0:

112 Moby Thesaurus words for "downturn":
   boom, bottoming out, business cycle, business fluctuations, bust,
   cascade, catabasis, cataract, chute, collapse, comedown,
   cooling off, crash, crisis, debacle, debasement, decadence,
   decadency, deceleration, declension, declination, decline,
   decline and fall, decrescendo, defluxion, deformation, degeneracy,
   degenerateness, degeneration, degradation, demotion, depravation,
   depravedness, depreciation, depression, derogation, descending,
   descension, descent, deterioration, devolution, diminuendo, dip,
   dive, down, downbend, downcome, downcurve, downfall, downflow,
   downgrade, downpour, downrush, downslide, downswing, downtrend,
   downward mobility, downward trend, drop, dropping, dwindling,
   dying, ebb, economic cycle, economic expansion, economic growth,
   effeteness, expanding economy, expansion, fading, failing, failure,
   failure of nerve, fall, falling, falling-off, falloff, gravitation,
   growth, high growth rate, inclination, involution, lapse,
   loss of tone, low, market expansion, peak, peaking, plummeting,
   plunge, pounce, prosperity, rapids, recession, recovery,
   regression, remission, retreat, retrocession, retrogradation,
   retrogression, sag, slip, slippage, slowdown, slump, stoop,
   subsidence, swoop, upturn, wane, waterfall