Green’s Dictionary of Slang

1. (US campus) annoyed, unhappy.

1986		Eble Campus Sl. Mar. 6: illing – problemsome or troublesome: George said bad things about Claude last night. George is illing bad. [Ibid.] Nov. 5: illin’ – in a perturbed state or bad mood.
1989		P. Munro Sl. U. 30: He was illin when he found out he didn’t pass his philosophy class.
1995		Eble Campus Sl. Dec.

2. (orig. US black/teen) acting or thinking wildly, aggressively, crazily.

1987		Arizona Dly Star (Tucson, AZ) Youth Beat 26 Dec. 8/4: Illing: Getting wild!
1989		P. Munro Sl. U. 30: be illin [...] to react inappropriately, to act stupid.
1992		R.C. Cruz Straight Outta Compton 27: That’s why you be illin’ all the time cause you just mad that your daddy lives in a jungle like a gorilla whenever your parents get together.
1997		Simon & Burns Corner (1998) 318: Fat Curt, for one, can tell from a man’s walk whether he’s flush, illing, or carrying a semiauto down in the dip of his sweats.
2002		‘Touré’ Portable Promised Land (ms.) 158: We Words (My Favorite Things) [...] You’re damn skippy. You’ll get nathan. You ripped it. You be illin.
2012		NY Times 12 Jan. 🌐 One of these references define the word illin’ as ‘stupid, insane’.

3. (US campus) in a difficult or unpleasant situation, under severe stress.

1986		Eble Campus Sl. Oct. 3: illing – generally bad.
1989		(con. 1982–6) T. Williams Cocaine Kids (1990) 137: illin suffering severe mental stress.

4. (US campus) drunk.

1988

Eble Campus Sl. Mar. 6: be illin’ – become drunk: We were illin’ like crazed weasels with a couple of crucial bowheads last night.

5. (US campus) unattractive, old-fashioned.

1989

Eble Campus Sl. Sept. 4: illin’ – [...] out of style: That dress she wore was illin’.

6. (US black) performing superbly.

1991		D. Jenkins You Gotta Play Hurt 273: ‘Draculer was clean tonight. Draculer be illin’, you know? Draculer strike like lightnin’’ .
1995		L. Stavsky et al. A2Z.