Grunge

google

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1960s (as a general term of disparagement): back-formation from grungy, perhaps suggested by grubby and dingy.

wiktionary

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Back-formation from  grungy. 

etymonline

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grunge (n.)

"sloppiness, dirtiness," also "untidy person," 1965, American English teen slang, probably a back-formation from grungy. In reference to the music and fashion style that originated in Seattle is attested from 1989.