The Collaborative International Dictionary of English v.0.48:

peepul \pee"pul\ (p[=e]"p[u^]l), Peepul tree \Pee"pul
tree`\(p[=e]"p[u^]l tr[=e]`). [Hind. p[imac]pal, Skr. pippala.]
   (Bot.)
   A sacred tree (Ficus religiosa) of the Buddhists, a kind of
   fig tree which attains great size and venerable age; it lacks
   the prop roots of the banyan. See Bo tree. [Written also
   pippul tree, and pipal tree.]

   Syn: pipal, peepul, peepul tree, pipal tree, pipul, sacred
        fig, bo tree, Ficus religiosa.
        [1913 Webster]

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):

Ficus religiosa
    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]