The Collaborative International Dictionary of English v.0.48:

Opobalsam \Op`o*bal"sam\, Opobalsamum \Op`o*bal"sa*mum\, n. [L.
   opobalsamum, Gr. ?; ? vegetable juice + ? balsam.] (Med.)
   The old name of the aromatic resinous juice of the
   Balsamodendron opobalsamum, now commonly called balm of
   Gilead. See under Balm.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Balm \Balm\ (b[aum]m), n. [OE. baume, OF. bausme, basme, F.
   baume, L. balsamum balsam, from Gr. ba`lsamon; perhaps of
   Semitic origin; cf. Heb. b[=a]s[=a]m. Cf. Balsam.]
   [1913 Webster]
   1. (Bot.) An aromatic plant of the genus Melissa.
      [1913 Webster]

   2. The resinous and aromatic exudation of certain trees or
      shrubs. --Dryden.
      [1913 Webster]

   3. Any fragrant ointment. --Shak.
      [1913 Webster]

   4. Anything that heals or that mitigates pain. "Balm for each
      ill." --Mrs. Hemans.
      [1913 Webster]

   Balm cricket (Zool.), the European cicada. --Tennyson.

   Balm of Gilead (Bot.), a small evergreen African and
      Asiatic tree of the terebinthine family (Balsamodendron
      Gileadense). Its leaves yield, when bruised, a strong
      aromatic scent; and from this tree is obtained the balm of
      Gilead of the shops, or balsam of Mecca. This has a
      yellowish or greenish color, a warm, bitterish, aromatic
      taste, and a fragrant smell. It is valued as an unguent
      and cosmetic by the Turks. The fragrant herb
      Dracocephalum Canariense is familiarly called balm of
      Gilead, and so are the American trees, Populus
      balsamifera, variety candicans (balsam poplar), and
      Abies balsamea (balsam fir).
      [1913 Webster]

WordNet (r) 3.0 (2006):

balm of Gilead
    n 1: medium-sized fir of northeastern North America; leaves
         smell of balsam when crushed; much used for pulpwood and
         Christmas trees [syn: balsam fir, balm of Gilead,
         Canada balsam, Abies balsamea]
    2: a fragrant oleoresin
    3: small evergreen tree of Africa and Asia; leaves have a strong
       aromatic odor when bruised [syn: balm of gilead,
       Commiphora meccanensis]