The Collaborative International Dictionary of English v.0.48:

Bodhisat \Bo"dhi*sat\, Bodhisattva \Bo`dhi*satt"va\, Bodhisattwa
\Bo`dhi*satt"wa\, n. [Skr. b[=o]dhisattva (perh. through Pali
   b[=o]dhisatt[=o]); fr. b[=o]dhi knowledge, enlightenment +
   sattva being, essence.] (Buddhism)
   One who has reached the highest degree of saintship, so that
   in his next incarnation he will be a Buddha, or savior of the
   world. -- Bo"dhi*sat`ship, n.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Bodhisattva
    n 1: Buddhist worthy of nirvana who postpones it to help others
         [syn: Bodhisattva, Boddhisatva]