loam. 1. a rich, friable soil containing a relatively equal mixture of sand and silt and a somewhat smaller proportion of clay. 2. a mixture of clay, sand, straw, etc., used in making molds for founding and in plastering walls, stopping holes, etc.3. earth or soil.oam. 1. a rich, friable soil containing a relatively equal mixture of sand and silt and a somewhat smaller proportion of clay. 2. a mixture of clay, sand, straw, etc., used in making molds for founding and in plastering walls, stopping holes, etc.