noun

1. a person who takes the part of or strongly supports one side, party, or person; often, specif., an unreasoning, emotional adherent
2. any of a group of guerrilla fighters; esp., a member of an organized civilian force fighting covertly to drive out occupying enemy troops

Etymology: MFr < It partigiano < parte < L pars, part

adjective

1. of, like, or characteristic of a partisan
2. blindly or unreasonably devoted
3. of or having to do with military partisans