The Collaborative International Dictionary of English v.0.48:

Pompom \Pom"pom`\, n.
   an ornamental ball or tuft of wool, feathers, or other fluffy
   material used as a decoration on clothing such as hats and
   slippers.
   [PJC]

   2. a pompon.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Pompon \Pom"pon\, n. [F.]
   1. Any trifling ornament for a woman's dress or bonnet.
      [1913 Webster]

   2. (Mil.) A tuft or ball of wool, or the like, sometimes worn
      by soldiers on the front of the hat (such as a shako),
      instead of a feather.
      [1913 Webster +PJC]

   3.
      (a) A hardy garden chrysanthemum having buttonlike heads
          of flowers.
      (b) Any of several dwarf varieties of the Provence rose.
          [Webster 1913 Suppl.]

   4. the globe-shaped flower head characteristic of certain
      plants such as dahlias and chrysanthemums.
      [PJC]

   5. a ball-shaped cluster of ribbons or streamers held in the
      hand and waved by some cheerleaders at team sports
      contests. See pompom girl. Called also pompom.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Pompom \Pom"pom`\, Pom-pom \Pom"-pom`\, n. [Imitative.] (Mil.)
   originally, a Vickers-Maxim one-pounder automatic machine
   cannon using metallic ammunition fed from a lopped belt
   attached to the gun; -- popularly so called from its peculiar
   drumming sound in action. More recently, the term is applied
   mostly to automatic antiaircraft cannons.
   [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

pom-pom
    n 1: decoration consisting of a ball of tufted wool or silk;
         usually worn on a hat [syn: pompon, pom-pom]
    2: artillery designed to shoot upward at airplanes [syn:
       antiaircraft, antiaircraft gun, flak, flack, pom-
       pom, ack-ack, ack-ack gun]