epi·some \ˈepəˌsōm\noun (-s) Etymology:epi- + -some (III) : a genetic determinant (as the DNA of some bacteriophages) that can replicate either autonomously in bacterial cytoplasm or as an integral part of their chromosomes — compare plasmid herein • epi·som·al\¦epə¦sōməl\adjective • epi·som·al·lyadverb • epi·so·mic\-ōmik\adjective