The Collaborative International Dictionary of English v.0.48:
Upmost \Up"most`\, a. [Cf. Uppermost.] Highest; topmost; uppermost. --Spenser. Dryden. [1913 Webster]WordNet (r) 3.0 (2006):
upmost adj 1: at or nearest to the top; "the uppermost book in the pile"; "on the topmost step" [syn: topmost, uppermost, upmost]