The Collaborative International Dictionary of English v.0.48:

Squalid \Squal"id\ (skw[o^]l"[i^]d), a. [L. squalidus, fr.
   squalere to be foul or filthy.]
   Dirty through neglect; foul; filthy; extremely dirty.
   [1913 Webster]

         Uncombed his locks, and squalid his attire. --Dryden.
   [1913 Webster]

         Those squalid dens, which are the reproach of large
         capitals.                                --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

squalid
    adj 1: morally degraded; "a seedy district"; "the seamy side of
           life"; "sleazy characters hanging around casinos";
           "sleazy storefronts with...dirt on the walls"- Seattle
           Weekly; "the sordid details of his orgies stank under his
           very nostrils"- James Joyce; "the squalid atmosphere of
           intrigue and betrayal" [syn: seamy, seedy, sleazy,
           sordid, squalid]
    2: foul and run-down and repulsive; "a flyblown bar on the edge
       of town"; "a squalid overcrowded apartment in the poorest
       part of town"; "squalid living conditions"; "sordid
       shantytowns" [syn: flyblown, squalid, sordid]

Moby Thesaurus II by Grady Ward, 1.0:

146 Moby Thesaurus words for "squalid":
   abject, abominable, arrant, atrocious, awful, base, beastly,
   beat-up, bedraggled, beggarly, beneath contempt, black,
   blameworthy, blowzy, broken-down, brutal, careless, cheesy,
   chintzy, contemptible, crummy, debased, degraded, deplorable,
   depraved, despicable, detestable, dilapidated, dingy, dire, dirty,
   disgusting, disheveled, disreputable, drabbletailed, draggled,
   draggletailed, dreadful, egregious, enormous, execrable, fetid,
   filthy, flagrant, foul, frowzy, frumpish, frumpy, fulsome, grave,
   grievous, gross, grubby, hateful, heinous, horrible, horrid,
   ignoble, impure, in rags, infamous, informal, lamentable, little,
   loathsome, loose, lousy, low, low-down, lumpen, mangy, mean,
   measly, messy, miserable, monstrous, mussy, nasty, nefarious,
   negligent, noisome, notorious, obnoxious, odious, offensive,
   outrageous, paltry, petty, pitiable, pitiful, poky, poor, ragged,
   raggedy, rank, regrettable, reprehensible, reptilian, repulsive,
   rotten, ruinous, run-down, sad, scabby, scandalous, schlock,
   scraggly, scrubby, scruffy, scummy, scurvy, seedy, shabby,
   shameful, shocking, shoddy, slack, slatternly, sleazy, slipshod,
   sloppy, slovenly, slumlike, slummy, sluttish, small, soily, sordid,
   tacky, tattered, terrible, too bad, ugly, unclean, uncleanly,
   unkempt, unmentionable, unneat, unsightly, untidy, vile,
   villainous, woeful, worst, worthless, wretched