Definition of progressist in US English:

progressist

noun

  • A person who favours or advocates progress, especially in political or social matters; a reformer, a progressive.

adjective

  • Favouring or characterized by innovation or reform; progressive.

Origin

Mid 19th century; earliest use found in The Times. From progress + -ist; in many instances after equivalent terms in Romance languages, as French progressiste, Spanish progresista, adjective and noun, Italian progressista, adjective and noun.