lemon vs Citrus limetta

lemon and Citrus limetta both are nouns.

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

As nouns, Citrus limetta is a hyponym of lemon; that is, Citrus limetta is a word with a more specific, narrower meaning than lemon:

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

Other hyponyms of lemon include sweet lemon, sweet lime.

lemon (noun)	Citrus limetta (noun)
an artifact (especially an automobile) that is defective or unsatisfactory	lemon tree having fruit with a somewhat insipid sweetish pulp
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