c. 1300, parlur, "apartment in a monastery for conversations with outside persons," earlier "window through which confessions were made" (c. 1200), from Old French parleor "courtroom, judgment hall, auditorium" (12c., Modern French parloir), from parler "to speak" (see parley (n.)).
The sense developed by late 14c. to "room off a main hall offering some privacy," by early 15c. to "public room of a private house," by 16c. to "the ordinary sitting room of a family." The meaning "show room for a business" (as in ice cream parlor) is by 1884. As an adjective, "advocating radical views from a position of comfort" (as in parlor socialist) is by 1900.