citrous fruit vs orange

citrous fruit and orange both are nouns.

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

As nouns, orange is a hyponym of citrous fruit; that is, orange is a word with a more specific, narrower meaning than citrous fruit:

citrous fruit: any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions
orange: round yellow to orange fruit of any of several citrus trees

Other hyponyms of citrous fruit include mandarin, mandarin orange, kumquat, lemon, lime, grapefruit, pomelo, shaddock, citrange, citron, calamondin.

citrous fruit (noun)	orange (noun)
any of numerous fruits of the genus Citrus having thick rind and juicy pulp; grown in warm regions	orange color or pigment; any of a range of colors between red and yellow
	round yellow to orange fruit of any of several citrus trees
	any citrus tree bearing oranges
	any pigment producing the orange color

citrous fruit (adjective)	orange (adjective)
	of the color between red and yellow; similar to the color of a ripe orange