sweet lemon vs lemon

sweet lemon and lemon both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet lemon	Yes	No	No	No
lemon	Yes	No	No	No

As nouns, lemon is a hypernym of sweet lemon; that is, lemon is a word with a broader meaning than sweet lemon:

sweet lemon: lemon tree having fruit with a somewhat insipid sweetish pulp
lemon: a small evergreen tree that originated in Asia but is widely cultivated for its fruit

Other hypernyms of sweet lemon include Citrus limon, lemon tree.

sweet lemon (noun)	lemon (noun)
lemon tree having fruit with a somewhat insipid sweetish pulp	an artifact (especially an automobile) that is defective or unsatisfactory
	a strong yellow color
	a distinctive tart flavor characteristic of lemons
	yellow oval fruit with juicy acidic flesh
	a small evergreen tree that originated in Asia but is widely cultivated for its fruit