Walkman vs stereo system

Walkman and stereo system both are nouns.

Word	Noun	Adjective	Verb	Adverb
Walkman	Yes	No	No	No
stereo system	Yes	No	No	No

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

Walkman: (trademark) a pocket-sized stereo system with light weight earphones
stereo system: 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, stereophonic system, stereophony.

Walkman (noun)	stereo system (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