The Collaborative International Dictionary of English v.0.48:

boilersuit \boilersuit\ n.
   a loose protective smock worn over ordinary clothing for
   dirty work. [British]

   Syn: overall, boilers suit.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

boilersuit
    n 1: a loose protective coverall or smock worn over ordinary
         clothing for dirty work [syn: overall, boilersuit,
         boilers suit]