Merriam-Webster Collegiate Dictionary - pom-pom

 I. noun  Etymology: alteration of pompon  Date: 1873  1. an ornamental ball or tuft used especially on clothing, caps, or costumes  2. a handheld usually brightly colored fluffy ball flourished by cheerleaders  II. noun  Etymology: imitative; from the sound of its discharge  Date: 1899 a multibarreled automatic antiaircraft gun of 20 to 40 millimeters mounted especially on ships