Noah Webster
Scrub
SCRUB, verb transitive [This word is probably formed on rub, or its root, and perhaps scrape, Latin scribo, may be from the same radix.]
To rub hard, either with the hand or with a cloth or an instrument; usually, to rub hard with a brush, or with something coarse or rough, for the purpose of cleaning, scouring or making bright; as, to scrub a floor; to scrub a deck; to scrub vessels of brass or other metal.
SCRUB, verb intransitive To be diligent and penurious; as, to scrub hard for a living.
SCRUB, noun
1. A mean fellow; one that labors hard and lives meanly.
2. Something small and mean.
No little scrub joint shall come on my board.
3. A worn out brush.