Definitions:

1. on a floor above adverb
   • they lived upstairs
2. on or of upper floors of a building adjective
   • the upstairs maid
3. the part of a building above the ground floor noun
   • no one was allowed to see the upstairs
4. with respect to the mind adverb
   • she's a bit weak upstairs

Synonyms:

• up the stairs
• upstair