Etymology 1

Noun

1. An adherent to a party or faction.
   • 1924: ARISTOTLE. Metaphysics. Translated by W. D. Ross. Nashotah, Wisconsin, USA: The Classical Library, 2001. Available at: . Book 1, Part 5.

     while Xenophanes, the first of these partisans of the One (for Parmenides is said to have been his pupil), gave no clear statement,

2. A fervent, sometimes militant, supporter or proponent of a party, cause, faction, person, or idea.
3. The commander of a body of detached light troops engaged in making forays and harassing an enemy.
4. Any member of such troops.

Adjective

1. Adherent to a party or faction; especially, having the character of blind, passionate, or unreasonable adherence to a party; as, blinded by partisan zeal.
2. Devoted to or biased in support of a party, group, or cause: partisan politics.
3. Serving as commander or member of a body of detached light troops: as, a partisan officer or corps.

Etymology 2

Noun

1. A spear with a triangular, double-edged blade.
2. A soldier armed with such a weapon.