The Collaborative International Dictionary of English v.0.48:
Lowermost \Low"er*most`\, a. [Irreg. superl. of Low. Cf. Uppermost, Foremost, etc.] Lowest. [1913 Webster]WordNet (r) 3.0 (2006):
lowermost adj 1: farthest down; "bottommost shelf" [syn: bottommost, lowermost, nethermost]