RhymeZone: freebase definitions

Definitions of freebase:

noun: (chemistry) The purified, dry form of an amine, especially an alkaloid natural product, that is normally used in solution.
noun: (specifically) The purified, dry form of certain illegal drugs, especially cocaine.
verb: To purify a drug by crystallization.
verb: To use a purified drug, especially cocaine, by heating it and inhaling the fumes produced.

(Definitions from Wiktionary)