The Collaborative International Dictionary of English v.0.48:
Topmost \Top"most`\, a. Highest; uppermost; as, the topmost cliff; the topmost branch of a tree. [1913 Webster] The nightngale may claim the topmost bough. --Cowper. [1913 Webster]WordNet (r) 3.0 (2006):
topmost adj 1: at or nearest to the top; "the uppermost book in the pile"; "on the topmost step" [syn: topmost, uppermost, upmost]