Wiktionary
plain work
n. 1 Basic, non-ornamental work; specifically (now (context historical English)) simple needlework. (from 13th c.) 2 (context masonry English) Smooth stonework without decoration or ornamentation. (from 15th c.)
Usage examples of "plain work".
Everyone had a curved knife stuck through a belt, and frequently a plain work knife as well.
Scores of people wandered the three levels of the interior, in groups or singly, most of them in plain work jumpers, but many in business suits or metanational uniforms, or in casual clothes, which these days consisted of loose pantaloons, blouses, and moccasins.
The fire flared high, picking their faces out of night, tinging plain work clothes with unrestful red, and then guttering down so that shadows swallowed the bodies.