alluvium (n.) Look up alluvium at Dictionary.com
"matter deposited by flowing water," 1660s, from noun use of Medieval Latin alluvium, neuter of alluvius "washed against," from Latin alluere "wash against," from ad "to, against" (see ad-) + -luere, comb. form of lavere "to wash" (from PIE root *leue- "to wash").