romaine vs cos

romaine and cos both are nouns.

Word	Noun	Adjective	Verb	Adverb
romaine	Yes	No	No	No
cos	Yes	No	No	No

As nouns, romaine and cos are synonyms defined as:

romaine and cos: lettuce with long dark-green leaves in a loosely packed elongated head

Other synonyms of romaine include cos lettuce, romaine lettuce.

romaine (noun)	cos (noun)
lettuce with long dark-green leaves in a loosely packed elongated head	lettuce with long dark-green leaves in a loosely packed elongated head
	ratio of the adjacent side to the hypotenuse of a right-angled triangle