noun

• (uncountable) A thicket or jungle, often specified by the name of the prevailing plant.
  "oak scrub"
• (uncountable) Vegetation judged to be of inferior quality or of little use to humans, though sometimes thick and impenetrable, growing in poor soil or in sand; also, brush.
• (countable, US, stock breeding) One of the common livestock of a region of no particular breed or not of pure breed, especially when inferior in size, etc.; particularly a male animal poorly suited for breeding.
• (countable, derogatory) One who labors hard and lives meanly; a mean fellow.
  "A sorry scrub, said Mr. High-mind."

verb

• (transitive) To rub hard; to wash with rubbing; usually, to rub with a wet brush, or with something coarse or rough, for the purpose of cleaning or brightening
  "to scrub a floor"
• (intransitive) To rub anything hard, especially with a wet brush; to scour
• (intransitive, figuratively) To be diligent and penurious
  "to scrub hard for a living"
• (transitive) To call off a scheduled event; to cancel.
  "Engineers had to scrub the satellite launch due to bad weather."

noun

• (medicine, in the plural) Clothing worn while performing surgery.
• (by extension, in the plural) Any medical uniform consisting of a short-sleeved shirt and pants (trousers).
  "A man dressed as a lab tech, his blue scrubs startlingly pale against the vivid red and black chaos, moved into sight from behind the SUV. He carried an assault rifle."
• (slang, obsolete) Informal attire or dress code; morning dress
  "The third, which was as homely as its name, and which she reserved for scouring the country and such like rough usage in quite private rural life, was her "Scrub.""