'episodic' originates from Greek, specifically the word 'epeisodion' (ἐπεισόδιον), where 'epi-' meant 'upon, in addition' and 'eisodion' (from 'eisodos') meant 'entrance' or 'coming in.'

'epeisodion' passed into later languages and gave rise to French/Latin forms that became English 'episode'; the adjective 'episodic' was formed from 'episode' (with the suffix -ic) in English, and the adverb 'episodically' was created by adding -ally.

Initially it referred to an inserted or incidental part (especially in drama or music); over time it evolved to mean 'occurring in separate or loosely connected incidents,' which is the modern sense used in 'episodically.'