WordNet (r) 3.0 (2006):

shortfall
    n 1: the property of being an amount by which something is less
         than expected or required; "new blood vessels bud out from
         the already dilated vascular bed to make up the nutritional
         deficit" [syn: deficit, shortage, shortfall]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "shortfall":
   absence, arrear, arrearage, arrears, beggary, decline, defalcation,
   default, defectiveness, deficiency, deficit, delinquency,
   deprivation, destitution, drought, failure, falling short, famine,
   imperfection, impoverishment, inadequacy, incompleteness,
   inferiority, insufficiency, lack, need, omission, short measure,
   shortage, shortcoming, slump, starvation, underage, want,
   wantage