citron vs citrus

citron and citrus both are nouns.

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

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

citron: large lemonlike fruit with thick aromatic rind; usually preserved
citrus: any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions

Other hypernyms of citron include citrous fruit, citrus fruit.

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

citron: thorny evergreen small tree or shrub of India widely cultivated for its large lemonlike fruits that have thick warty rind
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 citron include citrus tree.

citron (noun)	citrus (noun)
large lemonlike fruit with thick aromatic rind; usually preserved	any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions
thorny evergreen small tree or shrub of India widely cultivated for its large lemonlike fruits that have thick warty rind	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