jackhammer

from WordNet (r) 3.0 (2006)

jackhammer
    n 1: a hammer driven by compressed air [syn: {air hammer},
         {jackhammer}, {pneumatic hammer}]

from The Collaborative International Dictionary of English v.0.48

jackhammer \jackhammer\ n.
   a hammer having a strong steel cutting blade, driven by
   compressed air in multiple rapid strokes, and used for
   cutting through pavement, concrete, or other hard substances.

   Syn: air hammer, pneumatic hammer.
        [WordNet 1.5]