1. Relating to or consisting of any material that has been carried or deposited by running water: The result of the soil being washed away by water may result in an alluvial valley or an alluvial deposit, all of which consist of earth and sand that has been left by rivers, floods, etc.

The most alluvial deposits that have ever been recorded in Fred's community took place recently during the severe flooding.

2. Etymology: borrowed from Medieval Latin alluvium, alluvius, "washed against", from Latin alluere, "to wash against"; from al-, a form of ad- before l, "to, against", + -luere, a combining form of lavere, "to wash".