segregationist (n.)

1550s, "act of separating" (a sense now obsolete); 1610s, "act or action of segregating, separation from others," from Late Latin segregationem (nominative segregatio), noun of action from past-participle stem of segregare (see segregate). Meaning "state or condition of being segregated" is from 1660s. Specific U.S. sense of "enforced separation of races" is attested from 1883.

word-forming element meaning "one who does or makes," also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista (source also of Spanish, Portuguese, Italian -ista), from Greek agent-noun ending -istes, which is from -is-, ending of the stem of verbs in -izein, + agential suffix -tes.

Variant -ister (as in chorister, barrister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish, popularized in American English 1970s by names of Latin-American revolutionary movements.