ass - Wiktionary, the free dictionary

ass (countable and uncountable, plural asses) (vulgar, slang, US) Train compartment: two sick young junkies on their way to Lexington tear their pants down in convulsions of lust. One of them soaps his cock and works it up the other's ass with a corkscrew motion. That does it! Now listen!

Source: en.m.wiktionary.org