Last week we discussed how mistorin מסתורין is a Talmudic era "blend" of a Hebrew root and a Greek word. A more recent blend is the word gaon גאון. Let's take a look.
In Biblical Hebrew, gaon has a few different meanings - "glory, majesty", "pride, haughtiness" and "rising of the waters, tides." All of these meanings show a connection to the source of gaon - the root גאה, which means "to rise up, be proud", and is also the source of the word for pride - גאוה ga'ava.
The word is used in Nachum 2:3 (as well as Tehilim 47:5) in the positive sense of "pride":
כִּ֣י שָׁ֤ב ה' אֶת־גְּא֣וֹן יַעֲקֹ֔ב כִּגְא֖וֹן יִשְׂרָאֵ֑ל
"For the LORD has restored the Pride of Jacob, as well as the Pride of Israel"
Gaon Yaakov - "Pride of Jacob" was adopted as the name of a post Talmudic Babylonian yeshiva, and the head of that yeshiva, whose official title was Rosh Yeshivat Gaon Yaakov, was abbreviated to "Gaon". During this period the most important rabbinical leaders were known as geonim, some of the famous including Amram Gaon and Saadia Gaon.
The period of the Geonim ended around 1000 CE, but the title of gaon was continued to be used to describe individuals who had mastered the Torah. Such usage can be found in the poetry of Ibn Ezra and others, and perhaps most famously it was used to describe the 18th century rabbi Eliyahu of Vilna - the Vilna Gaon.
The blend I mentioned above occurred later. Gaon sounds similar to the word "genius" in many foreign languages. In addition to English, we find the German and French genie, Russian гений (geniy), and Yiddish zheni. So in Modern Hebrew gaon came to refer to a genius - indicating inherent intellectual ability, and not just proficiency in the study of Torah.
Within Modern Hebrew the adjective geoni גאוני - "ingenious" developed as well. I'll leave it up to you to decide whether or not this post fits that description!