The word is a modern English compound, built from two elements of distinct origins. The first, "triple," traces back to the Latin triplus, itself a combination of tri- (three) and -plus (fold), a suffix related to the idea of multiplication. The second, "decker," originates from the Middle Dutch dec (covering, roof), which entered English as "deck," referring to a ship's floor or platform. By adding the agentive suffix -er to "deck," English formed "decker" to denote something possessing a specific number of such levels. The compound "triple-decker" thus logically constructs its meaning from its components: a "three-fold thing having decks or levels," applied first to ships, then to buildings, vehicles, and finally, the iconic sandwich.

Structure: triple (threefold) + decker (having decks) - triple: From Latin triplus, from tri- (three) + -plus (fold). A combining form indicating threefold quantity or composition. - decker: From the English word deck (a floor or level) + the agent suffix -er. Functions as a noun-forming element meaning "something having (a specified number of) decks."