The Collaborative International Dictionary of English v.0.48:

Slum \Slum\ (sl[u^]m), n. [CF. Slump, n.]
   1. A foul back street of a city, especially one filled with a
      poor, dirty, degraded, and often vicious population; any
      low neighborhood or dark retreat; -- usually in the
      plural; as, Westminster slums are haunts for theives.
      --Dickens.
      [1913 Webster]

   2. pl. (Mining) Same as Slimes.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Slum \Slum\ (sl[u^]m), v. i.
   To visit or frequent slums, esp. out of curiosity, or for
   purposes of study, etc. Also called go slumming. [Colloq.]
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

slum
    n 1: a district of a city marked by poverty and inferior living
         conditions [syn: slum, slum area]
    v 1: spend time at a lower socio-economic level than one's own,
         motivated by curiosity or desire for adventure; usage
         considered condescending and insensitive; "attending a
         motion picture show by the upper class was considered
         sluming in the early 20th century"

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "slum":
   Augean stables, Bowery, Chinatown, East End, East Side,
   Little Hungary, Little Italy, West End, West Side, barrio,
   black ghetto, blighted area, business district, central city,
   city center, core, downtown, dump, ghetto, greenbelt, hole, hovel,
   inner city, midtown, muck, outskirts, pesthole, pigpen, pigsty,
   plague spot, red-light district, residential district, rookery,
   run-down neighborhood, shopping center, skid, skid road, skid row,
   slab, slums, stable, stew, sty, suburbia, suburbs, tenderloin,
   tenement, tenement district, the slums, uptown, urban blight,
   warren