nucleolus vs cell organ

nucleolus and cell organ both are nouns.

Word	Noun	Adjective	Verb	Adverb
nucleolus	Yes	No	No	No
cell organ	Yes	No	No	No

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

nucleolus: a small round body of protein in a cell nucleus; such organelles contain RNA and are involved in protein synthesis
cell organ: a specialized part of a cell; analogous to an organ

Other hypernyms of nucleolus include cell organelle, organelle.

nucleolus (noun)	cell organ (noun)
a small round body of protein in a cell nucleus; such organelles contain RNA and are involved in protein synthesis	a specialized part of a cell; analogous to an organ