A militant is someone who is vigorously active, combative, and/or aggressive, especially in support of a cause. The term is not associated with the military, and it can refer to an individual displaying aggressive behavior or attitudes. A militant can be anyone who subscribes to the idea of using vigorous, sometimes extreme, activity to achieve an objective, usually political. The term "militant" is sometimes used to describe groups that do not name or describe themselves as such.

As an adjective, "militant" means aggressively active (as in a cause) . It implies a disposition to dominate often in disregard of others rights or in determined and energetic pursuit of ones ends. Examples of usage include "militant reformers" or "militant conservationists".

As a noun, "militant" refers to a person who uses militant methods in pursuit of an objective. It can also be used as a euphemism for terrorist or armed insurgent.

In summary, a militant is someone who is actively and aggressively pursuing a cause, often using extreme methods to achieve their objectives.