frontier vs field of study

frontier and field of study both are nouns.

Word	Noun	Adjective	Verb	Adverb
frontier	Yes	No	No	No
field of study	Yes	No	No	No

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

frontier: an undeveloped field of study; a topic inviting research and development
field of study: a branch of knowledge

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

frontier (noun)	field of study (noun)
an undeveloped field of study; a topic inviting research and development	a branch of knowledge
a wilderness at the edge of a settled area of a country
an international boundary or the area (often fortified) immediately inside the boundary