"one practicing as an advocate in English courts of law," 1540s, from bar (n.3) in the legal sense + -ster. Also see attorney. The middle element is obscure. Related: Barristerial.
Entries linking to barrister
bar n.3
"whole body of lawyers, the legal profession," 1550s, a sense which derives ultimately from the railing that separated benchers from the hall in the Inns of Court (see bar (n.1)). Students who had attained a certain standing were "called" to it to take part in the important exercises of the house. After c. 1600, however, this was popularly assumed to mean the bar in a courtroom, the wooden railing marking off the area around the judge's seat, where prisoners stood for arraignment and where a barrister (q.v.) stood to plead. As the place where the business of court was done, bar in this sense had become synonymous with court by early 14c.
-ster
Old English -istre, from Proto-Germanic *-istrijon, feminine agent suffix used as the equivalent of masculine -ere (see -er (1)). Also used in Middle English to form nouns of action (meaning "a person who ...") without regard for gender.
The genderless agent noun use apparently was a broader application of the original feminine suffix, beginning in the north of England, but linguists disagree over whether this indicates female domination of weaving and baking trades, as represented in surnames such as Webster, Baxter, Brewster, etc. (though modern spinster probably carries an originally female ending).
Also compare whitester "one who bleaches cloth;" kempster (c. 1400; Halliwell has it as kembster) "woman who cleans wool." Chaucer ("Merchant's Tale") has chidester "an angry woman" (the 17c. had scoldster). Also compare Middle English shepster (late 14c.) "dressmaker, female cutter-out," literally "shapester," sleestere (mid-15c.) "murderess, female killer" ("slay-ster"). Sewster "seamstress" (Middle English seuestre, late 13c. as a surname, also used of men) is still in Jonson but was obsolete or provincial after 17c. In Modern English, the suffix has been productive in forming derivative nouns (gamester,roadster,punster, rodster "angler," etc.).