archegonium vs plant organ

archegonium and plant organ both are nouns.

Word	Noun	Adjective	Verb	Adverb
archegonium	Yes	No	No	No
plant organ	Yes	No	No	No

As nouns, plant organ is a hypernym of archegonium; that is, plant organ is a word with a broader meaning than archegonium:

archegonium: a female sex organ occurring in mosses, ferns, and most gymnosperms
plant organ: a functional and structural unit of a plant or fungus

archegonium (noun)	plant organ (noun)
a female sex organ occurring in mosses, ferns, and most gymnosperms	a functional and structural unit of a plant or fungus