1. Any of various eukaryotic organisms of the class Dictyostelia that exist as free-living amoeboid cells in the soil and under certain conditions aggregate into a mass that develops into a stalked sporangium. Also called cellular slime mold.

2. Any of various eukaryotic organisms of the class Myxogastria (formerly Myxomycetes) that develop from amoeboid cells into a large multinucleate plasmodium that produces stalked sporangia. Also called myxomycete, plasmodial slime mold.