iceberg vs crisphead lettuce

iceberg and crisphead lettuce both are nouns.

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

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

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

Other synonyms of iceberg include iceberg lettuce.

iceberg (noun)	crisphead lettuce (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