dingy adj.

late Old English dung "manure, decayed matter used to fertilize soil," from Proto-Germanic *dungō (source also of Old Frisian and Old Saxon dung "manure;" Old High German tunga "manuring," tung "underground room covered with manure;" German Dung; Old Norse dyngja "heap of manure, women's apartment;" Swedish dynga "dung, muck;" Danish dynge "heap, mass, pile"), perhaps from a PIE *dhengh- "covering" (source also of Lithuanian dengti "to cover," Old Irish dingim "I press").

The word recalls the ancient Germanic custom (reported by Tacitus) of covering underground shelters with manure to keep in warmth in winter. The meaning "animal excrement," whether used as fertilizer or not, is from late 13c.

It appears that the whole body of journeymen tailors is divided into two classes, denominated Flints and Dungs: the former work by the day and receive all equal wages; the latter work generally by the piece ["The Annual Register for the Year 1824," London, 1825].

Dung beetle, common name of the beetles which roll up balls of dung," is attested by 1630s. In colloquial American English, tumble-bug. An Old English word for it was tordwifel "turd weevil."

"sloppy, shabby," 1965, American English slang, perhaps based on, or blended from, grubby and dingy.