Why is the ninth month called September?
c.1600, "characterized by advancement" (in action, character, etc.), from progress (n.) + -ive, or else from French progressif, from past participle stem of Latin progredi. Of taxation, from 1889; of jazz, from 1947. Meaning "characterized by striving for change and innovation, avant-garde, liberal" is from 1908.
In the socio-political sense "favoring reform; radically liberal," it emerged in various British contexts from the 1880s; in the U.S. it was active as a movement in the 1890s and a generation thereafter, the name being taken again from time to time, most recently by some more liberal Democrats and other social activists, by c.2000. The noun in the sense "one who favors social and political change in the name of progress" is first attested 1865 (originally in Christianity). Earlier in a like sense were progressionist (1849, adjective; 1884, noun), progressist (1848). Related: Progressively; progressiveness.
progressive pro·gres·sive (prə-grěs'ĭv)
Moving forward; advancing.
Proceeding in steps; continuing steadily by increments, as of a course of treatment.
Tending to become more severe or wider in scope, as of a disease or paralysis.