Walkman vs stereophony

Walkman and stereophony both are nouns.

Word	Noun	Adjective	Verb	Adverb
Walkman	Yes	No	No	No
stereophony	Yes	No	No	No

As nouns, stereophony is a hypernym of Walkman; that is, stereophony is a word with a broader meaning than Walkman:

Walkman: (trademark) a pocket-sized stereo system with light weight earphones
stereophony: reproducer in which two microphones feed two or more loudspeakers to give a three-dimensional effect to the sound

Other hypernyms of Walkman include stereo, stereo system, stereophonic system.

Walkman (noun)	stereophony (noun)
(trademark) a pocket-sized stereo system with light weight earphones	reproducer in which two microphones feed two or more loudspeakers to give a three-dimensional effect to the sound