partisanship Definition

partisan
noun

1. An enthusiastic supporter of a party, person, cause, etc.

Thesaurus: follower, supporter, backer, champion, devotee, disciple, factionary.
2. A member of an armed resistance group in a country occupied by an enemy.

adj

1. Strongly loyal to one side, especially blindly so; biased.

Thesaurus: factional, biased, prejudiced, discriminatory, one-sided, predisposed, sectarian, slanted; disinterested, fair.

Derivative: partisanship
noun

Etymology: 16c: French, from parte part.