noun
- the doctrine or practice of vigorous action or involvement as a means of achieving political or other goals, sometimes by demonstrations, protests, etc.
- Philosophy.
- a theory that the essence of reality is pure activity, especially spiritual activity, or process.
- a theory that the relationship between the mind and the objects of perception depends upon the action of the mind.
noun
- a policy of taking direct and often militant action to achieve an end, esp a political or social one
1920 in the political sense; see activist + -ism. Earlier (1907) it was used in reference to a philosophical theory.