rate of return vs ROI

rate of return and ROI both are nouns.

Word	Noun	Adjective	Verb	Adverb
rate of return	Yes	No	No	No
ROI	Yes	No	No	No

As nouns, ROI is a hyponym of rate of return; that is, ROI is a word with a more specific, narrower meaning than rate of return:

rate of return: the amount returned per unit of time expressed as a percentage of the cost
ROI: (corporate finance) the amount, expressed as a percentage, that is earned on a company's total capital calculated by dividing the total capital into earnings before interest, taxes, or dividends are paid

Other hyponyms of rate of return include return on invested capital, return on investment.

rate of return (noun)	ROI (noun)
the amount returned per unit of time expressed as a percentage of the cost	(corporate finance) the amount, expressed as a percentage, that is earned on a company's total capital calculated by dividing the total capital into earnings before interest, taxes, or dividends are paid