downstairs

Adjective

• on or of lower floors of a building
  • the downstairs (or downstair) phone
    

Adverb

• on a floor below
  • the tenants live downstairs
    

Related words

• Synonyms: 
  downstair , down the stairs , on a lower floor , below
• Antonyms: 
  upstairs , upstair , up the stairs , on a higher floor