Dingy

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mid 18th century: perhaps based on Old English dynge ‘dung’.

wiktionary

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From English dialectal (Kentish) dingy(“dirty”), of unknown origin, though probably from an unrecorded Middle English *dingy, *düngy, from Old English *dyncgiġ(“covered with dung, dirty”), an umlaut form of Old English duncge, dung(“dung”), equivalent to dung +‎ -y. [1]

dingy (plural dingies)

etymonline

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dingy (adj.)

1736, in Kentish dialect, "dirty, foul," a word of uncertain origin, but perhaps related to dung. Meaning "soiled, tarnished, having a dull, brownish color" (from grime or weathering) is by 1751; hence "shabby, shady, drab" (by 1855). The noun dinge "dinginess" (1816) is a back-formation; as a derogatory word for "black person, Negro," by 1848. Related: Dingily; dinginess.