Plaining

c.1300, "flat, smooth," from O.Fr. plain, from L. planus "flat, even, level" (see plane (1)). Sense of "evident" is from, c.1300; meaning "simple, sincere, ordinary" is recorded from c.1374. In ref. to the dress and speech of Quakers, it is recorded from 1827; of Amish and Mennonites, from 1904. Of appearance, as a euphemism for "ill-favored, ugly" it dates from 1749. Plain Jane "unattractive woman" first attested 1912. Plain-spoken first attested 1678. Plain clothes "ordinary dress" (as opposed to military uniform) is from 1822; of police detectives, it is attested from 1842. Plain-song (1513) translates L. cantus planus.