daydreaming vs oneirism

daydreaming and oneirism both are nouns.

Word	Noun	Adjective	Verb	Adverb
daydreaming	Yes	No	No	No
oneirism	Yes	No	No	No

As nouns, daydreaming and oneirism are synonyms defined as:

Other synonyms of daydreaming include air castle, castle in Spain, castle in the air, daydream, reverie, revery.

daydreaming (noun)	oneirism (noun)
absentminded dreaming while awake	absentminded dreaming while awake