iceberg lettuce vs iceberg

iceberg lettuce and iceberg both are nouns.

Word	Noun	Adjective	Verb	Adverb
iceberg lettuce	Yes	No	No	No
iceberg	Yes	No	No	No

As nouns, iceberg lettuce and iceberg are synonyms defined as:

iceberg lettuce and iceberg: lettuce with crisp tightly packed light-green leaves in a firm head

Other synonyms of iceberg lettuce include crisphead lettuce.

iceberg lettuce (noun)	iceberg (noun)
lettuce with crisp tightly packed light-green leaves in a firm head	lettuce with crisp tightly packed light-green leaves in a firm head
	a large mass of ice floating at sea; usually broken off of a polar glacier