The Collaborative International Dictionary of English v.0.48:

blue-collar \blue-collar\ adj.
   1. of or designating work or workers in industry not
      requiring well-groomed appearance. [Narrower terms:
      industrial] white-collar
      [WordNet 1.5]

   2. of those who work for wages especially manual or
      industrial laborers. [Narrower terms: lower-class,
      low-class]

   Syn: propertyless, wage-earning, working-class.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

blue-collar
    adj 1: of or designating manual industrial work or workers [ant:
           white-collar]
    2: of those who work for wages especially manual or industrial
       laborers; "party of the propertyless proletariat"- G.B.Shaw
       [syn: propertyless, wage-earning, working-class, blue-
       collar]