yolk vs vitellus

yolk and vitellus both are nouns.

Word	Noun	Adjective	Verb	Adverb
yolk	Yes	No	No	No
vitellus	Yes	No	No	No

As nouns, yolk and vitellus are synonyms defined as:

yolk and vitellus: nutritive material of an ovum stored for the nutrition of an embryo (especially the yellow mass of a bird or reptile egg)

yolk (noun)	vitellus (noun)
nutritive material of an ovum stored for the nutrition of an embryo (especially the yellow mass of a bird or reptile egg)	nutritive material of an ovum stored for the nutrition of an embryo (especially the yellow mass of a bird or reptile egg)
the yellow spherical part of an egg that is surrounded by the albumen