iceberg vs lettuce

iceberg and lettuce both are nouns.

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

As nouns, lettuce is a hypernym of iceberg; that is, lettuce is a word with a broader meaning than iceberg:

iceberg: lettuce with crisp tightly packed light-green leaves in a firm head
lettuce: leaves of any of various plants of Lactuca sativa

iceberg (noun)	lettuce (noun)
lettuce with crisp tightly packed light-green leaves in a firm head	leaves of any of various plants of Lactuca sativa
a large mass of ice floating at sea; usually broken off of a polar glacier	any of various plants of the genus Lactuca
	informal terms for money