lemon vs citrus

lemon and citrus both are nouns.

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

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

lemon: yellow oval fruit with juicy acidic flesh
citrus: any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions

Other hypernyms of lemon include citrous fruit, citrus fruit.

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

lemon: a small evergreen tree that originated in Asia but is widely cultivated for its fruit
citrus: any of numerous tropical usually thorny evergreen trees of the genus Citrus having leathery evergreen leaves and widely cultivated for their juicy edible fruits having leathery aromatic rinds

Other hypernyms of lemon include citrus tree.

lemon (noun)	citrus (noun)
an artifact (especially an automobile) that is defective or unsatisfactory	any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions
a strong yellow color	any of numerous tropical usually thorny evergreen trees of the genus Citrus having leathery evergreen leaves and widely cultivated for their juicy edible fruits having leathery aromatic rinds
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