NOUN (4)

1. (anatomy) a somewhat rounded subdivision of a bodily organ or part;
- Example: "ear lobe"

2. (botany) a part into which a leaf is divided;

3. the enhanced response of an antenna in a given direction as indicated by a loop in its radiation pattern;

4. a rounded projection that is part of a larger structure;

The Collaborative International Dictionary of English v.0.48:

Lobe \Lobe\ (l[=o]b), n. [F. lobe, Gr. lobo`s.]
   Any projection or division, especially one of a somewhat
   rounded form; as:
   (a) (Bot.) A rounded projection or division of a leaf.
       --Gray.
   (b) (Zool.) A membranous flap on the sides of the toes of
       certain birds, as the coot.
   (c) (Anat.) A round projecting part of an organ, as of the
       liver, lungs, brain, etc. See Illust. of Brain.
   (b) (Mach.) The projecting part of a cam wheel or of a
       non-circular gear wheel.
       [1913 Webster]

   Lobe of the ear, the soft, fleshy prominence in which the
      human ear terminates below, also called the earlobe.
      See. Illust. of Ear.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

lobe
    n 1: (anatomy) a somewhat rounded subdivision of a bodily organ
         or part; "ear lobe"
    2: (botany) a part into which a leaf is divided
    3: the enhanced response of an antenna in a given direction as
       indicated by a loop in its radiation pattern
    4: a rounded projection that is part of a larger structure