music lesson vs lesson

music lesson and lesson both are nouns.

Word	Noun	Adjective	Verb	Adverb
music lesson	Yes	No	No	No
lesson	Yes	No	No	No

As nouns, lesson is a hypernym of music lesson; that is, lesson is a word with a broader meaning than music lesson:

music lesson (noun)	lesson (noun)
a lesson in performing music	a task assigned for individual study
	a unit of instruction
	punishment intended as a warning to others
	the significance of a story or event