three-decker vs triple-decker

three-decker and triple-decker both are nouns.

Word	Noun	Adjective	Verb	Adverb
three-decker	Yes	No	No	No
triple-decker	Yes	No	No	No

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

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

Other synonyms of three-decker include club sandwich.

three-decker (noun)	triple-decker (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