• upstaairs,
• upstaires,
• ypstair,
• hpstair,
• jpstair,
• ipstair,
• 8pstair,
• 7pstair,
• uostair,
• ulstair,
• u-stair,
• u0stair,
• upatair,
• upztair,
• upxtair,
• updtair,
• up-stair,
• upstairs,
• Upstaite,
• upstaeirs

• upstage,
• upstanding,
• upstream,
• upstairs,
• upset,
• upstate,
• upstroke,
• upstager,
• upstart.

The adjective form of the word "upstairs" is "upstairs".

The plural form of "upstair" is "upstairs"

The singular form of the word "upstair" is "upstairs"