The Collaborative International Dictionary of English v.0.48:

Bo tree \Bo" tree`\ (Bot.)
   The peepul tree; esp., the very ancient tree standing at
   Anurajahpoora in Ceylon, grown from a slip of the tree under
   which Gautama is said to have received the heavenly light and
   so to have become Buddha.
   [1913 Webster]

         The sacred bo tree of the Buddhists (Ficus
         religiosa), which is planted close to every temple,
         and attracts almost as much veneration as the status of
         the god himself. . . . It differs from the banyan
         (Ficus Indica) by sending down no roots from its
         branches.                                --Tennent.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bo tree
    n 1: fig tree of India noted for great size and longevity; lacks
         the prop roots of the banyan; regarded as sacred by
         Buddhists [syn: pipal, pipal tree, pipul, peepul,
         sacred fig, bo tree, Ficus religiosa]