Green’s Dictionary of Slang

1. sticky, dirty, unpleasant substances.

1969		Current Sl. III:4 6: Grunge, n. A bad, unpleasant thing, specially food.
1975		G. Underwood ‘Razorback Sl.’ in AS L:1/2 61: There’s grunge in the bottom of my Dr. Pepper bottle!
1988		D. Woodrell Muscle for the Wing 52: His mouth tasted like barroom floor grunge.
2003		Arvigo & Epstein Spiritual Bathing 67: The attendant administered the most harsh and vigorous scrub [...] and streams of grunge and dirt rolled off. ...

2. (also grunger) a general term of abuse, a repugnant, odious, dirty or boring person or thing.

1967–8		Baker et al. CUSS.
1978		Eble Campus Sl. Apr. 2: grunge – something dull or unappealing. The work for the course was a real grunge.
1999		R.G. Barrett Wind & Monkey (2013) [ebook] It was some kind of grunge crime writing [...] pretty fuckin ordinary.
1999		Guardian Media 2 Aug. 2: What about the Spectator writers who regularly describe female Guardian journalists as ‘grungers and groaners’.
2000		Indep. Rev. 20 May 1: Pure grunge still reigns around Deptford.

3. a form of rock music, epitomized by the work of the Seattle band Nirvana, but first used in relation to the New York Dolls, c.1973 (also known, among many rivals, as the ‘godfathers of punk’).

1973		New Yorker 19 Nov. 234: Your average American rock-and-roll fan can stand the Dolls’ brand of high-strung urban grunge only if it comes from somewhere besides New York—preferably England.
1991		B. Hamper Rivethead (1992) 195: Our own little grunge quartet called Dr. Schwarz Kult.
2000		Guardian Rev. 21 Jan. 18: Grunge deliberately looked and sounded as dingy, abrasive and piss-awful as its perpetrators.

4. the fashion style that developed out of the rock music, favouring a dishevelled appearance.

1994

J. Wambaugh Finnegan’s Week 160: Most of the hardbodies wore combinations of Day-glo shorts, tank tops [...] and cutoffs. There was a bit of hip-hop and grunge.