The noun partisan is an individual who is a firm or strong supporter of a person, a cause, or a group. This word can also be an adjective which means showing a strong bias or emotional allegiance to a principle, a political party, or a person.
Synonyms are one-sided, prejudiced, sympathetic, or devotee.
The word origins from the Middle French (15th century) partisan borrowed from dialectal upper Italian partezan (Tuscan partigiano) meaning “member of a faction, partner” and parte meaning “part, party”. It also comes from Latin partem (nominative pars) “a part, piece, a share, a division, a party or faction, a part of the body, a fraction, a function, office”.
I bumped into a partisan earlier who was carrying the candidate’s banner.
The partisans managed to rally at a scorching hot weather which gave the policemen terrible headaches.
The teacher showed a biased and partisan behavior towards his favorite student.