1. A compound produced by the mixing of two or more chemicals.

  2. A compound formed by the fusion of two molecules (or, less often, atoms) which are then held together by a coordinate covalent bond.

  3. A complex that forms when a chemical binds to a biological molecule, such as DNA or protein.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.