The Collaborative International Dictionary of English v.0.48:
Diluvium \Di*lu"vi*um\, n.; pl. E. Diluviums, L. Diluvia. [L. diluvium. See Dilute, Deluge.] (Geol.) A deposit of superficial loam, sand, gravel, stones, etc., caused by former action of flowing waters, or the melting of glacial ice. [1913 Webster] Note: The accumulation of matter by the ordinary operation of water is termed alluvium. [1913 Webster]