The Collaborative International Dictionary of English v.0.48:

Upstairs \Up*stairs"\, adv.
   Up the stairs; in or toward an upper story.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Upstairs \Up"stairs`\, a.
   Being above stairs; as, an upstairs room.
   [1913 Webster]

WordNet (r) 3.0 (2006):

upstairs
    adv 1: on a floor above; "they lived upstairs" [syn: upstairs,
           up the stairs, on a higher floor] [ant: below,
           down the stairs, downstairs, on a lower floor]
    2: with respect to the mind; "she's a bit weak upstairs"
    adj 1: on or of upper floors of a building; "the upstairs maid";
           "an upstairs room" [syn: upstairs, upstair] [ant:
           downstair, downstairs]
    n 1: the part of a building above the ground floor; "no one was
         allowed to see the upstairs"

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "upstairs":
   above, abovestairs, airward, aloft, aloof, heavenward, high,
   high up, in the air, in the clouds, on high, on stilts,
   on the peak, on tiptoe, over, overhead, skyward, straight up,
   tiptoe, to the zenith, up, up attic, up north, up steps, upalong,
   uphill, uphillward, uplong, upstream, upstreamward, uptown, upward,
   upwards, upwith