From what I could quickly gather the first reference to (אדון(י is when Sarah laughed to herself after overhearing what יי said to Abraham in Bereshith 18:12. The English translation uses a lower cased "lord or husband" as translated in my Chumash. In modern Hebrew אדון can be used for the English "sir, mister, master, lord." If you understand the נְקֻדּוֹת (niqqudot) in modern Hebrew, this question can easily rabbit hole into eternity. The Hebrew roots of these words are the guiding lights, אדון has a root of דון.
In regards to רבון, I could only find a root variable of רבון in scripture thus far. In Daniel 9:18 it is stated לֹ֣א עַל־צִדְקֹתֵ֗ינוּ אֲנַ֨חְנוּ מַפִּילִ֤ים תַּחֲנוּנֵ֙ינוּ֙ לְפָנֶ֔יךָ כִּ֖י עַל־רַחֲמֶ֥יךָ הָרַבִּֽים׃; or Not because of any merit of ours do we lay our plea before You but because of Your abundant mercies. The root variable of רִבּוֹן is הָרַבִּֽים or abundant in English. In modern Hebrew words such as "gentlemen, maximum, and interest (banking) also share the same root, רבב. If you wish to dive deeper into רבון, this is a great place to find sources from TaNaKh.
With all that being said, it would seem that the difference depends; Do you speak/read Hebrew?