The Collaborative International Dictionary of English v.0.48:

Scrub \Scrub\ (skr[u^]b), a.
   Mean; dirty; contemptible; scrubby.
   [1913 Webster]

         How solitary, how scrub, does this town look!
                                                  --Walpole.
   [1913 Webster]

         No little scrub joint shall come on my board. --Swift.
   [1913 Webster]

   Scrub game, a game, as of ball, by unpracticed players.

   Scrub race, a race between scrubs, or between untrained
      animals or contestants.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Scrub \Scrub\ (skr[u^]b), v. t. [imp. & p. p. Scrubbed
   (skr[u^]bd); p. pr. & vb. n. Scrubbing.] [OE. scrobben,
   probably of Dutch or Scand. origin; cf. Dan. skrubbe, Sw.
   skrubba, D. schrobben, LG. schrubben.]
   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; as, to scrub a floor, a doorplate.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Scrub \Scrub\ (skr[u^]b), v. i.
   To rub anything hard, especially with a wet brush; to scour;
   hence, to be diligent and penurious; as, to scrub hard for a
   living.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Scrub \Scrub\ (skr[u^]b), n.
   1. One who labors hard and lives meanly; a mean fellow. "A
      sorry scrub." --Bunyan.
      [1913 Webster]

            We should go there in as proper a manner as
            possible; nor altogether like the scrubs about us.
                                                  --Goldsmith.
      [1913 Webster]

   2. Something small and mean.
      [1913 Webster]

   3. A worn-out brush. --Ainsworth.
      [1913 Webster]

   4. A thicket or jungle, often specified by the name of the
      prevailing plant; as, oak scrub, palmetto scrub, etc.
      [1913 Webster]

   5. (Stock Breeding) One of the common live stock of a region
      of no particular breed or not of pure breed, esp. when
      inferior in size, etc. [U.S.]
      [1913 Webster]

   6. Vegetation of inferior quality, though sometimes thick and
      impenetrable, growing in poor soil or in sand; also,
      brush; -- called also scrub brush. See Brush, above.
      [Australia & South Africa]
      [Webster 1913 Suppl. +PJC]

   7. (Forestry) A low, straggling tree of inferior quality.
      [Webster 1913 Suppl.]

   Scrub bird (Zool.), an Australian passerine bird of the
      family Atrichornithidae, as Atrichia clamosa; --
      called also brush bird.

   Scrub oak (Bot.), the popular name of several dwarfish
      species of oak. The scrub oak of New England and the
      Middle States is Quercus ilicifolia, a scraggy shrub;
      that of the Southern States is a small tree (Quercus
      Catesbaei); that of the Rocky Mountain region is Quercus
      undulata, var. Gambelii.

   Scrub robin (Zool.), an Australian singing bird of the
      genus Drymodes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

scrub
    adj 1: (of domestic animals) not selectively bred
    n 1: dense vegetation consisting of stunted trees or bushes
         [syn: scrub, chaparral, bush]
    2: the act of cleaning a surface by rubbing it with a brush and
       soap and water [syn: scrub, scrubbing, scouring]
    v 1: clean with hard rubbing; "She scrubbed his back" [syn:
         scrub, scour]
    2: wash thoroughly; "surgeons must scrub prior to an operation"
       [syn: scrub, scrub up]
    3: postpone indefinitely or annul something that was scheduled;
       "Call off the engagement"; "cancel the dinner party"; "we had
       to scrub our vacation plans"; "scratch that meeting--the
       chair is ill" [syn: cancel, call off, scratch, scrub]