Adjective downstairs has 1 sense
  1. downstairs, downstair - on or of lower floors of a building; "the downstairs (or downstair) phone"
    Antonyms: upstairs, upstair
,Adverbial downstairs has 1 sense
  1. downstairs, down the stairs, on a lower floor, below - on a floor below; "the tenants live downstairs"
    Antonyms: upstairs, up the stairs, on a higher floor
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