episode vs happening

episode and happening both are nouns.

Word	Noun	Adjective	Verb	Adverb
episode	Yes	No	No	No
happening	Yes	No	No	No

As nouns, happening is a hypernym of episode; that is, happening is a word with a broader meaning than episode:

Other hypernyms of episode include natural event, occurrence, occurrent.

episode (noun)	happening (noun)
film consisting of a succession of related shots that develop a given subject in a movie	an event that happens
a part of a broadcast serial
a brief section of a literary or dramatic work that forms part of a connected series
a happening that is distinctive in a series of related events