WordNet (r) 3.0 (2006):

underprivileged
    adj 1: lacking the rights and advantages of other members of
           society [ant: privileged]

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "underprivileged":
   badly off, beggared, beggarly, bereaved, bereft, chronic poor,
   chronic poverty area, common, demeaning, depressed,
   depressed class, depressed population, deprived, dire,
   disadvantaged, donsie, doomful, evil-starred, fatal, fleeced,
   fortuneless, funest, ghetto-dwellers, ghettoized, handicapped,
   hapless, humble, ill off, ill-fated, ill-starred, impoverished,
   in adverse circumstances, in need, in rags, in the shade, in want,
   inauspicious, indigent, inferior, infra dig, junior, less, lesser,
   low, lower, lowly, luckless, mendicant, minor, modest, necessitous,
   needy, ominous, on relief, ordinary, out at elbows, out of luck,
   outcasts, pauperized, planet-struck, poor, poverty subculture,
   poverty-stricken, sad, second rank, second string, secondary,
   servile, short of luck, slum-dwellers, star-crossed, starveling,
   stripped, sub, subaltern, subject, subordinate, subservient,
   the disadvantaged, the dispossessed, the distressed,
   the down-and-out, the forgotten man, the have-nots, the needy,
   the other America, the poor, the powerless, the underprivileged,
   the urban poor, third rank, third string, unblessed,
   underdeveloped nation, unfortunate, unhappy, unlucky, unprosperous,
   unprovidential, vulgar, welfare rolls