Source : Webster's Revised Unabridged Dictionary (1913)

Navvy \Nav"vy\, n.; pl. {Navies}. [Abbreviated fr. navigator.]
   Originally, a laborer on canals for internal navigation;
   hence, a laborer on other public works, as in building
   railroads, embankments, etc. [Eng.]

Source : WordNet®

navvy
     n : a laborer who is obliged to do menial work [syn: {drudge}, {peon},
          {galley slave}]