root hair vs plant organ

root hair and plant organ both are nouns.

Word	Noun	Adjective	Verb	Adverb
root hair	Yes	No	No	No
plant organ	Yes	No	No	No

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

root hair: thin hairlike outgrowth of an epidermal cell just behind the tip; absorbs nutrients from the soil
plant organ: a functional and structural unit of a plant or fungus

root hair (noun)	plant organ (noun)
thin hairlike outgrowth of an epidermal cell just behind the tip; absorbs nutrients from the soil	a functional and structural unit of a plant or fungus