1. (in pharmacology) A substance added to a drug to speed or increase the action of the main component.
  2. (in immunology) A substance (such as aluminium hydroxide) or an organism (such as bovine tuberculosis bacillus) which increases the response to an antigen.
PAC, 1993, 65, 2003. 'Glossary for chemists of terms used in toxicology (IUPAC Recommendations 1993)' on page 2010 (