The Collaborative International Dictionary of English v.0.48:

pitsaw \pit"saw\ n.
   A large two-handed saw formerly used to cut logs into planks;
   one man stood above the log and the other in a pit below.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

pitsaw
    n 1: a large two-handed saw formerly used to cut logs into
         planks; one man stood above the log and the other in a pit
         below