Green’s Dictionary of Slang

(drugs) to intensify the effect of cocaine by heating it in combination with ether or other chemicals before inhaling.

1984		W.D. Myers Motown and Didi 25: [H]e was [...] twisting around to find a vein and telling himself that at least he would never freebase.
1989		T. Blacker Fixx 305: Some tosspot freebasing in the library.
1999		Guardian Rev. 17 Sept. 3: They were freebasing cocaine. So I thought I’d try some.
2000		Observer Rev. 13 Feb. 4: My mate Narrow and I had been freebasing in my flat for five hours non-stop.
2010		K. Richards Life 417: Belushi [...] was freebasing.