Definition of three-decker in US English:

three-decker

noun

  • 1A thing with three levels or layers.

    as modifier ‘three-decker sandwiches’
    • ‘The deserts are similarly cloying and sticky, although a couple of them (the passion-fruit-meringue pie and a towering, three-decker coconut flan) are compulsively edible.’
    • ‘That night we ate over the water at a three-decker restaurant with exquisite food and atmosphere.’
    1. 1.1historical A sailing warship with three gun decks.

Pronunciation

three-decker

/ˈTHrēˌdekər//ˈθriˌdɛkər/