WordNet (r) 3.0 (2006):

palm tree
    n 1: any plant of the family Palmae having an unbranched trunk
         crowned by large pinnate or palmate leaves [syn: palm,
         palm tree]

Easton's 1897 Bible Dictionary:

Palm tree
   (Heb. tamar), the date-palm characteristic of Palestine. It is
   described as "flourishing" (Ps. 92:12), tall (Cant. 7:7),
   "upright" (Jer. 10:5). Its branches are a symbol of victory
   (Rev. 7:9). "Rising with slender stem 40 or 50, at times even
   80, feet aloft, its only branches, the feathery, snow-like,
   pale-green fronds from 6 to 12 feet long, bending from its top,
   the palm attracts the eye wherever it is seen." The whole land
   of Palestine was called by the Greeks and Romans Phoenicia,
   i.e., "the land of palms." Tadmor in the desert was called by
   the Greeks and Romans Palmyra, i.e., "the city of palms." The
   finest specimens of this tree grew at Jericho (Deut. 34:3) and
   Engedi and along the banks of the Jordan. Branches of the palm
   tree were carried at the feast of Tabernacles (Lev. 23:40). At
   our Lord's triumphal entrance into Jerusalem the crowds took
   palm branches, and went forth to meet him, crying, "Hosanna:
   Blessed is the King of Israel that cometh in the name of the
   Lord" (Matt. 21:8; John 12:13). (See DATE.)