Egyptian onion vs Allium cepa

Egyptian onion and Allium cepa both are nouns.

Word	Noun	Adjective	Verb	Adverb
Egyptian onion	Yes	No	No	No
Allium cepa	Yes	No	No	No

As nouns, Allium cepa is a hypernym of Egyptian onion; that is, Allium cepa is a word with a broader meaning than Egyptian onion:

Egyptian onion: type of perennial onion grown chiefly as a curiosity or for early salad onions; having bulbils that replace the flowers
Allium cepa: bulbous plant having hollow leaves cultivated worldwide for its rounded edible bulb

Other hypernyms of Egyptian onion include onion, onion plant.

Egyptian onion (noun)	Allium cepa (noun)
type of perennial onion grown chiefly as a curiosity or for early salad onions; having bulbils that replace the flowers	bulbous plant having hollow leaves cultivated worldwide for its rounded edible bulb