episome
noun
epi·some ˈe-pə-ˌsōm 
-ˌzōm
: a genetic determinant (such as the DNA of some bacteriophages) that can replicate autonomously in bacterial cytoplasm or as an integral part of the chromosomes
episomal
ˌe-pə-ˈsō-məl
adjective -ˈzō-
episomally
ˌe-pə-ˈsō-mə-lē
adverb -ˈzō-
Example Sentences
Recent Examples on the Web The latent virus may integrate into the human genome – as does HIV, for example – or exist in the nucleus as a self-replicating piece of DNA called an episome. 
William Petri, The Conversation, 31 July 2020
William Petri, The Conversation, 31 July 2020 Word History
Etymology
borrowed from French épisome, from épi- epi- + -some -some entry 3
Note: The term was introduced by the French biologists François Jacob (1920-2013) and Élie Wollman (1917-2008) in "Les épisomes, éléments génétiques ajoutés," Comptes rendus hebdomadaires des séances de l'Académie des Sciences, tome 247, première partie (juillet-septembre 1958), séance du 7 juillet 1958, pp. 154-56.
First Known Use
circa 1931, in the meaning defined above
Medical Definition
episome
noun
epi·some ˈep-ə-ˌsōm -ˌzōm
-ˌzōm : 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