The Collaborative International Dictionary of English v.0.48:

batholith \bath"o*lith\ (b[a^]th"[-o]*l[i^]th), n. [Gr. baqo`s
   depth + -lith.]
   A large mass of intrusive igneous rock believed to have
   solidified deep within the earth.

   Syn: batholite, pluton, plutonic rock.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

batholith
    n 1: large mass of intrusive igneous rock believed to have
         solidified deep within the earth [syn: batholith,
         batholite, pluton, plutonic rock]