cos lettuce vs romaine

cos lettuce and romaine both are nouns.

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

As nouns, cos lettuce and romaine are synonyms defined as:

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

Other synonyms of cos lettuce include cos, romaine lettuce.

cos lettuce (noun)	romaine (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
lettuce with long dark-green spoon-shaped leaves