pomelo vs citrous fruit

pomelo and citrous fruit both are nouns.

Word	Noun	Adjective	Verb	Adverb
pomelo	Yes	No	No	No
citrous fruit	Yes	No	No	No

As nouns, citrous fruit is a hypernym of pomelo; that is, citrous fruit is a word with a broader meaning than pomelo:

pomelo: large pear-shaped fruit similar to grapefruit but with coarse dry pulp
citrous fruit: any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions

Other hypernyms of pomelo include citrus, citrus fruit.

pomelo (noun)	citrous fruit (noun)
large pear-shaped fruit similar to grapefruit but with coarse dry pulp	any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions
southeastern Asian tree producing large fruits resembling grapefruits