plain

plain simple, uncomplicated.
plain as a pikestaff very plain. The phrase was originally (in the mid 16th century) plain as a packstaff, a packstaff being the staff on which a pedlar supported his wares while resting.
plain living and high thinking denoting a frugal and philosophic lifestyle; the original allusion is to Wordsworth's lines ‘Plain living and high thinking are no more: The homely beauty of the good old cause Is gone.’
Plain People the Amish, the Mennonites, and the Dunkers, three strict Christian sects emphasizing a simple way of life.
plain sailing used to describe a process or activity which goes well and is easy and uncomplicated. The phrase, which is mid 18th century, is probably a popular use of plane sailing, denoting the practice of determining a ship's position on the theory that it is moving on a plane.

plain¹ / plān/ • adj. 1. not decorated or elaborate; simple or ordinary in character: good plain food everyone dined at a plain wooden table. ∎  without a pattern; in only one color: a plain fabric. ∎  bearing no indication as to source, contents, or affiliation: donations can be put in a plain envelope. ∎  (of a person) having no pretensions; not remarkable or special: a plain, honest man with no nonsense about him. ∎  (of a person) without a special title or status: for years he was just plain Bill. 2. easy to perceive or understand; clear: the advantages were plain to see it was plain that something was very wrong. ∎  (of written or spoken usage) clearly expressed, without the use of technical or abstruse terms: written in plain English. ∎  not using concealment or deception; frank: he recalled her plain speaking. 3. (of a person) not beautiful or attractive: the dark-haired, rather plain woman. 4. sheer; simple (used for emphasis): the main problem is just plain exhaustion. • adv. inf. clearly; unequivocally (used for emphasis): perhaps the youth was just plain stupid. • n. a large area of flat land with few trees. Compare with prairie. ∎  (the Plains) another term for Great Plains. PHRASES: as plain as the nose on one's face inf. very obvious. plain and simple inf. used to emphasize the statement preceding or following: she was a genius, plain and simple. plain as day inf. very clearly.DERIVATIVES: plain·ness n. plain² • v. [intr.] archaic mourn; lament. ∎  complain. ∎  emit a mournful or plaintive sound.

plain clear, manifest XIII; †flat, level, even; unembellished; free from duplicity or ambiguity XIV; ordinary, simple XVI. — OF. plain, fem. -e :— L. plānus, -a, f. base *plā- flat, of obscure orig.
Hence plainly XIV. So plain sb. flat tract of country. XIII. OF. plain (superseded by plaine :— L. coll. n. pl.) :— L. plānum, sb. use of n. of adj.. See also PLANE3, PLANE4.