episode (n.)

1670s, "commentary between two choric songs in a Greek tragedy," also "an incidental narrative or digression within a story, poem, etc.," from French épisode or directly from Greek epeisodion "an episode," literally "an addition," noun use of neuter of epeisodios "coming in besides," from epi "in addition" (see epi-) + eisodos "a coming in, entrance" (from PIE root *en "in").

The second element is a compound of eis "into" + hodos "a way, path; a journey; a method, system," a word of uncertain origin (see Exodus). Transferred sense of "outstanding incident, experience" first recorded in English 1773. Transferred by 1930s to individual broadcasts of serial radio programs.