1. Excessive zeal; fanaticism; that is, an unwillingness to recognize and respect differences in the opinions or beliefs of others.
2. Excessive intolerance of opposing views.
3. A reference to zeal in excess, referring to cases where activism and ambition in relation to an ideology have become excessive to the point of being harmful to others, oneself, and one's own cause.

While "excess of zeal" may be used to refer to very common and individual instances of excess, zealotry tends to be reserved for cases where excess zeal is shared with others, and has formed, or merged, with some kind of dogma; typically with ideological self-perpetuation as being among its primary foundations.

The recommended use of force and violence to propagate the ideology, is a common characteristic of this kind of self-perpetuation; perhaps inline with the "ends justify the means" rationale.