understairs From WikiWord, the free dictionary English Contents DefinitionsRelated wordsReferences DefinitionsnounA basement or cellar constructed, or accessed, from underneath the stairs. Related wordsSynonymsbasementbackstairsbackstairundercroftdownunderroombasement apartmentunderkeepsouterraincellarstairsdownstairsvaultsubstructionundergroundcellarage References Wiktionary — understairs Wikipedia — understairs