The Collaborative International Dictionary of English v.0.48:
Nethermost \Neth"er*most`\ (n[e^][th]"[~e]r*m[=o]st`), a. [AS. ni[eth]emest. See Nether, and cf. Aftermost.] Lowest; as, the nethermost abyss. --Milton. [1913 Webster]WordNet (r) 3.0 (2006):
nethermost adj 1: farthest down; "bottommost shelf" [syn: bottommost, lowermost, nethermost]