pomelo vs citrus fruit

pomelo and citrus fruit both are nouns.

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

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

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

Other hypernyms of pomelo include citrous fruit, citrus.

pomelo (noun)	citrus 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