kumquat vs citrous fruit

kumquat and citrous fruit both are nouns.

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

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

kumquat: small oval citrus fruit with thin sweet rind and very acid pulp
citrous fruit: any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions

Other hypernyms of kumquat include citrus, citrus fruit.

kumquat (noun)	citrous fruit (noun)
small oval citrus fruit with thin sweet rind and very acid pulp	any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions
any of several trees or shrubs of the genus Fortunella bearing small orange-colored edible fruits with thick sweet-flavored skin and sour pulp