lemon vs Citrus limon

lemon and Citrus limon both are nouns.

Word	Noun	Adjective	Verb	Adverb
lemon	Yes	No	No	No
Citrus limon	Yes	No	No	No

As nouns, lemon and Citrus limon are synonyms defined as:

lemon and Citrus limon: a small evergreen tree that originated in Asia but is widely cultivated for its fruit

Other synonyms of lemon include lemon tree.

lemon (noun)	Citrus limon (noun)
an artifact (especially an automobile) that is defective or unsatisfactory	a small evergreen tree that originated in Asia but is widely cultivated for its fruit
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