1. A condition of antagonism between organisms, especially micro-organisms (antonym of symbiosis).
2. The antagonistic association between two organisms in which one species adversely affects the other, often by production of a toxin.
3. An association of two organisms which is detrimental to one of them, in contrast to probiosis.
4. Production of an antibiotic by bacteria or other organisms inhibitory to other living things, especially among soil microbes.