- an active hostility or opposition, as between unfriendly or conflicting groups: the antagonism between the liberal and the conservative parties.
- an opposing force, principle, or tendency: Her plan to become an actress met with the antagonism of her family.
- an opposing action, as by one muscle in relation to another.
- the opposing action of substances, as drugs, that when taken together decrease the effectiveness of at least one of them (contrasted with synergism).
- Ecology.
- a relationship between two species of organisms in which the individuals of each species adversely affect the other, as in competition.
- the inhibition of the growth of one type of organism by a different type that is competing for the same ecological niche.
- openly expressed and usually mutual opposition
- the inhibiting or nullifying action of one substance or organism on another
- the normal opposition between certain muscles
- the inhibition or interference of growth of one kind of organism by another
