Source : Webster's Revised Unabridged Dictionary (1913)

Upside \Up"side`\, n.
   The upper side; the part that is uppermost.

   {To be upsides with}, to be even with. [Prov. Eng. & Scot.]
      --Sir W. Scott. --T. Hughes.

   {Upside down}. [Perhaps a corruption of OE. up so down,
      literally, up as down.] With the upper part undermost;
      hence, in confusion; in complete disorder; topsy-turvy.
      --Shak.

            These that have turned the world upside down are
            come hither also.                     --Acts xvii.
                                                  6.

Source : WordNet®

upside
     n : the highest or uppermost side of anything; "put your books
         on top of the desk"; "only the top side of the box was
         painted" [syn: {top}, {top side}, {upper side}]