Congregation Adath Jeshurun was created in 1906.
Congregation Kehilath Jeshurun was created in 1872.
Congregation Adath Israel Brith Sholom was created in 1842.
Elie Wiesel is still alive today, and is still working to educate people of all ages on the Holocaust, and how we need to learn from history.
Since you don't give any details of where you know this word from, and in what language it is, I'll try to tell you what I know and hope that's what you wanted. I know of a Hebrew word "Adah" (pronounced "Eidah"), which means "Congregation" (usually in a religious context). It can also mean a group of people from the same place or practising the same customs - religious or otherwise. The "th" at the end of the word is grammatical, and is used whenever there is a noun after the term "Adath", like in "Congregation Shalo'm", which would be "Adath Shalo'm", or any other name, whatever the name of that particular congregation is.
Beuronese Congregation was created in 1863.
Swiss Congregation was created in 1602.
Solesmes Congregation was created in 1837.
Dead Congregation was created in 2004.
Congregation Solel was created in 1957.
A Congregation of Ghosts was created in 2009.
Bavarian Congregation was created in 1684.
Congregation for Borders was created in 1627.