specialist (n.)

c. 1200, "given or granted in unusual circumstances, exceptional;" also "specific" as opposed to general or common; from Old French special, especial "special, particular, unusual" (12c., Modern French spécial) and directly from Latin specialis "individual, particular" (source also of Spanish especial, Italian speziale), from species "appearance, kind, sort" (see species).

Meaning "marked off from others by some distinguishing quality; dear, favored" is recorded from c. 1300. Also from c. 1300 is the sense of "selected for an important task; specially chosen." From mid-14c. as "extraordinary, distinguished, having a distinctive character," on the notion of "used for special occasions;" hence "excellent; precious."

From late 14c. as "individual, particular; characteristic." The meaning "limited as to function, operation, or purpose" is from 14c., but developed especially in the 19c. Special effects first attested 1951. Special interest in U.S. political sense is from 1910. Special pleading is recorded by 1680s, a term that had a sound legal meaning once but now is used generally and imprecisely. Special education in reference to those whose learning is impeded by some mental or physical handicap is from 1972.

Special pleading. (a) The allegation of special or new matter, as distinguished from a direct denial of matter previously alleged on the other side. ... (c) In popular use, the specious but unsound or unfair argumentation of one whose aim is victory rather than truth. [Century Dictionary]

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.

1610s, "one who generalizes," from general (adj.) + -ist. From 1894 as "one who engages in general studies" (opposed to specialist).