Green’s Dictionary of Slang

1. (W.I.) a general intensifier, both positive and negative.

[1734		J. Gay Distressd Wife II viii: You are Beast enough to be fond of the Country, I find, and I am to be lugg’d thither to keep you Company].
1956		S. Selvon Lonely Londoners 20: Moses sure is some test who living in London a long, long time and accustom to the beast winter.
1997–2001		Online Sl. Dict. 🌐 beast [...] adj 1. very good, excellent; COOL, AWESOME. (‘That concert was beast!’).

2. white; pertaining to white culture.

1999

(con. 1979–80) A. Wheatle Brixton Rock (2004) 2: I don’t want no beast food.

3. (US campus) excellent.

1997–2002		Hope College ‘Dict. of New Terms’ 🌐 beast adj. The best. Term used between friends to say something is awesome or to show their approval. ‘That new album is beast! I have to buy it!’ ‘Beast! I can’t believe you guys did that for me.’.
2017		theculturetrip.com ‘Guide to London Slang 10 Jan. 🌐 Beast – an adjective to describe something that’s really cool.