The Collaborative International Dictionary of English v.0.48:

chainsaw \chain"saw`\ (ch[=a]n"s[add]), n.
   a portable power saw having teeth that are linked to form an
   endless chain, rotated about two pivot points by a power
   mechanism, such as an electric motor or a gasoline engine.

   Note: They are used to efficiently cut trees, logs, or thick
         branches out of doors.

   Syn: chain saw.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

chainsaw
    n 1: portable power saw; teeth linked to form an endless chain
         [syn: chain saw, chainsaw]