fibril vs rhizoid

fibril and rhizoid both are nouns.

Word	Noun	Adjective	Verb	Adverb
fibril	Yes	No	No	No
rhizoid	Yes	No	No	No

As nouns, rhizoid is a hyponym of fibril; that is, rhizoid is a word with a more specific, narrower meaning than fibril:

fibril: a very slender natural or synthetic fiber
rhizoid: any of various slender filaments that function as roots in mosses and ferns and fungi etc

Other hyponyms of fibril include barb, cobweb, gossamer, chromatid, myofibril, myofibrilla, sarcostyle, hypha, paraphysis.

fibril (noun)	rhizoid (noun)
a very slender natural or synthetic fiber	any of various slender filaments that function as roots in mosses and ferns and fungi etc