green onion vs spring onion

green onion and spring onion both are nouns.

Word	Noun	Adjective	Verb	Adverb
green onion	Yes	No	No	No
spring onion	Yes	No	No	No

As nouns, green onion and spring onion are synonyms defined as:

green onion and spring onion: a young onion before the bulb has enlarged; eaten in salads

Other synonyms of green onion include scallion.

green onion (noun)	spring onion (noun)
a young onion before the bulb has enlarged; eaten in salads	a young onion before the bulb has enlarged; eaten in salads