the pipal, or sacred fig tree, Ficus religiosa, of India, under which the founder of Buddhism is reputed to have attained the Enlightenment that constituted him the Buddha.
1681, from Sinhalese bo, from Pali bodhi short for bodhi-taru "bo tree," lit. "tree of wisdom or enlightenment" (related to Skt. buddhah "awakened") + taru "tree."
[boh] 
