The Collaborative International Dictionary of English v.0.48:

Free base \Free" base`\ (fr[=e]" b[=a]s`), n.
   1. (Chem.) The basic form of an organic amine which is
      capable of forming acid salts such as hydrochlorides.
      [PJC]

   2. The basic form of a drug, often more powerful than a salt
      form because it is more readily absorbed into the blood
      stream.
      [PJC] free-base

The Collaborative International Dictionary of English v.0.48:

free-base \free-base\, Free base \Free" base`\(fr[=e]" b[=a]s`),
   v. i.
   To ingest the basic form of a narcotic drug, usually by
   injection.
   [PJC]