This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
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adj. downstairs

adj. on or of the lower floors of a building, especially the ground floor. Opposite of upstairs.

adj. on or of lower floors of a building

"The downstair is more of a casual, bistro type restaurant."

ground floor    downstairs   

glassless    driver's-side    bottle glass    arrow-slit    leaded-glass