refresher vs course of study

refresher and course of study both are nouns.

Word	Noun	Adjective	Verb	Adverb
refresher	Yes	No	No	No
course of study	Yes	No	No	No

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

refresher: a course that reviews and updates a topic for those who have not kept abreast of developments
course of study: education imparted in a series of lessons or meetings

Other hypernyms of refresher include class, course, course of instruction.

refresher (noun)	course of study (noun)
a course that reviews and updates a topic for those who have not kept abreast of developments	education imparted in a series of lessons or meetings
a drink that refreshes	an integrated course of academic studies
a fee (in addition to that marked on the brief) paid to counsel in a case that lasts more than one day