batholite 1. A large mass of intrusive igneous rock believed to have solidified deep within the earth. 2. A large emplacement of igneous intrusive (also called plutonic) rock that forms from cooled magma deep in the earth's crust. Batholiths are composed of multiple masses, or plutons, of magma that moved toward the surface from a zone of partial... Found on http://www.wordinfo.info/words/index/info/view_unit/1096/