three-decker vs club sandwich

three-decker and club sandwich both are nouns.

Word	Noun	Adjective	Verb	Adverb
three-decker	Yes	No	No	No
club sandwich	Yes	No	No	No

As nouns, three-decker and club sandwich are synonyms defined as:

three-decker and club sandwich: made with three slices of usually toasted bread

Other synonyms of three-decker include triple-decker.

three-decker (noun)	club sandwich (noun)
a warship carrying guns on three decks	made with three slices of usually toasted bread
any ship having three decks
made with three slices of usually toasted bread