Welsh onion vs Japanese leek

Welsh onion and Japanese leek both are nouns.

Word	Noun	Adjective	Verb	Adverb
Welsh onion	Yes	No	No	No
Japanese leek	Yes	No	No	No

As nouns, Welsh onion and Japanese leek are synonyms defined as:

Welsh onion and Japanese leek: Asiatic onion with slender bulbs; used as early green onions

Other synonyms of Welsh onion include Allium fistulosum.

Welsh onion (noun)	Japanese leek (noun)
Asiatic onion with slender bulbs; used as early green onions	Asiatic onion with slender bulbs; used as early green onions