from The American Heritage® Dictionary of the English Language, 4th Edition
- A trademark used for a pocket-sized cassette player, compact disk player, radio, or combined unit with lightweight earphones.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A portable audio cassette player with headphones.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. (trademark) a pocket-sized stereo system with light weight earphones
A trademark; apparently from walk + man. (Wiktionary)