futurology vs subject field

futurology and subject field both are nouns.

Word	Noun	Adjective	Verb	Adverb
futurology	Yes	No	No	No
subject field	Yes	No	No	No

As nouns, subject field is a hypernym of futurology; that is, subject field is a word with a broader meaning than futurology:

futurology: the study or prediction of future developments on the basis of existing conditions
subject field: a branch of knowledge

Other hypernyms of futurology include bailiwick, discipline, field, field of study, study, subject, subject area.

futurology (noun)	subject field (noun)
the study or prediction of future developments on the basis of existing conditions	a branch of knowledge