al·lu·vi·al I. \əˈlüvēəl, -vyəl also aˈ- or əlˈyü- or alˈyü-\adjective alsoal·lu·vi·an\-ən\ Etymology:alluvium + -al or -an 1.: relating to or composed of alluvium < alluvial soil > < an alluvial divide > 2.: found in alluvium < alluvial diamonds > II. noun (-s) 1. a.: alluvial soil b.Australia: gold-bearing alluvial soil 2.: a mineral occurring in placer deposits