Combined effect of two or more factors which is smaller than the solitary effect of
any one of those factors. In bioassays, the term may be used when a specified response
is produced by exposure to either of two factors but not by exposure to both together.
Source:
PAC, 1993, 65, 2003
(Glossary for chemists of terms used in toxicology (IUPAC Recommendations 1993))
on page 2014