Welsh onion vs Allium fistulosum

Welsh onion and Allium fistulosum both are nouns.

Word	Noun	Adjective	Verb	Adverb
Welsh onion	Yes	No	No	No
Allium fistulosum	Yes	No	No	No

As nouns, Welsh onion and Allium fistulosum are synonyms defined as:

Welsh onion and Allium fistulosum: Asiatic onion with slender bulbs; used as early green onions

Other synonyms of Welsh onion include Japanese leek.

Welsh onion (noun)	Allium fistulosum (noun)
Asiatic onion with slender bulbs; used as early green onions	Asiatic onion with slender bulbs; used as early green onions