Green’s Dictionary of Slang

good, excellent.

1988		Eble Campus Sl. Mar. 3: chillin’ – first rate: You’re a real chillin’ dude.
1997–2001		Online Sl. Dict. 🌐 chilling adj 1. fun. (‘That movie was chilling.’).
2000		Observer Mag. 27 Feb. 23: ‘It’s chillin’,’ he says [...] ‘It’s the real joint, OK?’.