alluvium
Concise Oxford English Dictionary © 2008 Oxford University Press:
alluvium /əˈl(j)uːvɪəm/
▶noun a deposit of clay, silt, and sand left by flowing flood water in a river valley or delta, typically producing fertile soil.
– derivatives
alluvial adjective.
alluvial adjective.
– origin C17: L., neut. of alluvius ‘washed against’, from ad- ‘towards’ + luere ‘to wash’.
'alluvium' also found in these Oxford entries:

