Source : Webster's Revised Unabridged Dictionary (1913)

Upmost \Up"most`\, a. [Cf. {Uppermost}.]
   Highest; topmost; uppermost. --Spenser. Dryden.

Source : WordNet®

upmost
     adj : at or nearest to the top; "the uppermost book in the pile";
           "on the topmost step" [syn: {topmost}, {uppermost}]