antagonism

noun

1. an active hostility or opposition, as between unfriendly or conflicting groups: the antagonism between the liberal and the conservative parties.
2. an opposing force, principle, or tendency: Her plan to become an actress met with the antagonism of her family.
3. Physiology. an opposing action, as by one muscle in relation to another.
4. Biochemistry, Pharmacology. the opposing action of substances, as drugs, that when taken together decrease the effectiveness of at least one of them (contrasted with synergism).
5. Ecology.
   1. a relationship between two species of organisms in which the individuals of each species adversely affect the other, as in competition.
   2. the inhibition of the growth of one type of organism by a different type that is competing for the same ecological niche.

noun

1. openly expressed and usually mutual opposition
2. the inhibiting or nullifying action of one substance or organism on another
3. physiol the normal opposition between certain muscles
4. biology the inhibition or interference of growth of one kind of organism by another

n.

1. Mutual opposition in action between structures, agents, diseases, or physiological processes.mutual resistance