synergism(An ecological association in which the physiological processes of behaviour of an individual are enhanced by the nearby presence of another organism)
synergistic effect of toxic substances(1. A state in which the combined effect of two or more substances is greater than the sum of the separate effects. 2. An effect whereby two toxic substance together have more of an impact than anticipated)
synthetic detergent(An artificially produced solid or liquid cleansing substance that acts like soap but is stronger, and is capable of dissolving oily materials and dispersing them in water)