sea onion vs squill

sea onion and squill both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea onion	Yes	No	No	No
squill	Yes	No	No	No

As nouns, squill is a hypernym of sea onion; that is, squill is a word with a broader meaning than sea onion:

sea onion: European scilla with small blue or purple flowers
squill: an Old World plant of the genus Scilla having narrow basal leaves and pink or blue or white racemose flowers

Other hypernyms of sea onion include scilla.

As nouns, sea onion and squill are synonyms defined as:

sea onion and squill: having dense spikes of small white flowers and yielding a bulb with medicinal properties

Other synonyms of sea onion include sea squill, Urginea maritima.

sea onion (noun)	squill (noun)
European scilla with small blue or purple flowers	an Old World plant of the genus Scilla having narrow basal leaves and pink or blue or white racemose flowers
having dense spikes of small white flowers and yielding a bulb with medicinal properties	having dense spikes of small white flowers and yielding a bulb with medicinal properties
	bulb of the sea squill, which is sliced, dried, and used as an expectorant