systems theory vs study

systems theory and study both are nouns.

Word	Noun	Adjective	Verb	Adverb
systems theory	Yes	No	No	No
study	Yes	No	Yes	No

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

systems theory: the interdisciplinary study of systems in general, with the goal of elucidating principles that can be applied to all types of systems at all nesting levels in all fields of research.
study: a branch of knowledge

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

systems theory (noun)	study (noun)
the interdisciplinary study of systems in general, with the goal of elucidating principles that can be applied to all types of systems at all nesting levels in all fields of research.	a detailed critical inspection
	a room used for reading and writing and studying
	preliminary drawing for later elaboration
	attentive consideration and meditation
	a branch of knowledge
	applying the mind to learning and understanding a subject (especially by reading)
	a state of deep mental absorption
	a written document describing the findings of some individual or group
	a composition intended to develop one aspect of the performer's technique
	someone who memorizes quickly and easily (as the lines for a part in a play)

systems theory (verb)	study (verb)
	be a student of a certain subject
	learn by reading books
	consider in detail and subject to an analysis in order to discover essential features or meaning
	be a student; follow a course of study; be enrolled at an institute of learning
	think intently and at length, as for spiritual purposes
	give careful consideration to