undercutter

noun5

1. •
   One who, or that which, undercuts.
2. •
   A type of plough with a V-shaped blade or sweep pulled along under the soil.
3. •
   A type of bit.
4. •
   A device for excavation, used on railways.

   • […] train of dump cars hauled behind undercutter machine loads rear car first, then ones ahead of it. Using undercutter avoids need for removing track. — 1962
5. •
   A device for cutting into rock walls from below.

   • The top and bottom portions of the machine are exactly alike and it may consequently be turned over and employed as an overcutter as well as an undercutter. — 1926