I. ˌəp-ˈsterz adverb
Date: 1584
1. : up the stairs : on or to a higher floor
2. : to or at a high altitude or higher position
kicked upstairs to company management
3. : in the head : intellectually
a little slow upstairs — Tom Clancy
II. ˈəp-ˈsterz adjective
Date: 1782
: situated above the stairs especially on an upper floor
an upstairs bedroom
III. ˈəp-ˈsterz, ˈəp-ˌ noun plural but singular or plural in construction
Date: 1842
: the part of a building above the ground floor