The Collaborative International Dictionary of English v.0.48:

Impoverish \Im*pov"er*ish\, v. t. [imp. & p. p. Impoverished;
   p. pr. & vb. n. Impoverishing.] [OF. empovrir; pref. em-
   (L. in) + povre poor, F. pauvre; cf. OF. apovrir, F.
   appauvrir, where the prefix is a-, L. ad. Cf. Empoverish,
   and see Poor, and -ish.]
   1. To make poor; to reduce to poverty or indigence; as,
      misfortune and disease impoverish families.
      [1913 Webster]

   2. To exhaust the strength, richness, or fertility of; to
      make sterile; as, to impoverish land.
      [1913 Webster]

WordNet (r) 3.0 (2006):

impoverished
    adj 1: poor enough to need help from others [syn: destitute,
           impoverished, indigent, necessitous, needy,
           poverty-stricken]
    2: destroyed financially; "the broken fortunes of the family"
       [syn: broken, wiped out(p), impoverished]

Moby Thesaurus II by Grady Ward, 1.0:

122 Moby Thesaurus words for "impoverished":
   Lenten, Spartan, ablated, abstemious, ascetic, austere, badly off,
   bankrupt, bare-handed, barren, beggared, beggarly, bereaved,
   bereft, burnt up, consumed, denuded, depleted, deprived, desolate,
   destitute, disadvantaged, dissipated, drained, dwarfed, dwarfish,
   eaten up, effete, empty, empty-handed, eroded, exhausted, exiguous,
   famished, finished, flat broke, fleeced, frugal, ghettoized, gone,
   half-starved, ill off, ill-equipped, ill-furnished, ill-provided,
   impecunious, in distress, in need, in rags, in want, indigent,
   insolvent, jejune, lean, limited, meager, mean, mendicant, miserly,
   narrow, necessitous, needy, niggardly, on relief, on short commons,
   out at elbows, paltry, parsimonious, pauperized, penurious,
   pinched, poor, poverty-stricken, puny, ruined, scant, scanty,
   scrawny, scrimp, scrimpy, short, shorthanded, skimp, skimpy,
   slender, slight, slim, small, spare, sparing, spent, starvation,
   starved, starveling, starving, stingy, stinted, stone-broke,
   straitened, strapped, stripped, stunted, subsistence, thin,
   underfed, undermanned, undernourished, underprivileged, unfed,
   unnourishing, unnutritious, unprovided, unreplenished, unsupplied,
   up against it, used up, wasted, watered, watery, wiped out,
   worn away, worn-out