In early use often hardly more emphatic than the mod. dirty; it is now a violent expression of disgust, seldom employed in polite colloquial speech. [OED]
Related: Filthily; filthiness.
1590s, from French squalide and directly from Latin squalidus "rough, coated with dirt, filthy," related to squales "filth," squalus "filthy," squalare "be covered with a rough, stiff layer, be coated with dirt, be filthy," of uncertain origin. Related: Squalidly; squalidness; squalidity.
"very filthy," 1590s, in reference to Augean stable, the cleansing of which was one of the labors of Hercules, from Greek Augeias, from Augeas, king of Elis, whose proverbially filthy stable contained 3,000 oxen and had gone uncleansed for 30 years. Hercules purified it in one day by turning the river Alpheus through it. The name probably is from auge "splendor, sunlight."
late 14c., "dung, excrement, feces; filth, dirt," from Old French ordure "filth, uncleanliness" (12c.), from ord, ort "filthy, dirty, foul," from Latin horridus "dreadful" (see horrid). Related: Ordurous.