castle in Spain vs daydreaming

castle in Spain and daydreaming both are nouns.

Word	Noun	Adjective	Verb	Adverb
castle in Spain	Yes	No	No	No
daydreaming	Yes	No	No	No

As nouns, castle in Spain and daydreaming are synonyms defined as:

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

castle in Spain (noun)	daydreaming (noun)
absentminded dreaming while awake	absentminded dreaming while awake