He was rabbi of the Jewish Status Quo Community in his town and author of over 20 books on rabbinical subjects, including the following (all were printed in Satu Mare):
Hebrew Torah Journal Ohel Yitzchok (1903–1914)
Hebrew Book Zichron L'Yisroel (1912)
Hebrew Torah Journal Sefer Hamagid (1928–1934)
Hebrew Torah Journal Magid Yeruchem (1925–1930)
Hebrew Book Kol Ha'chatan (1937)Klein's mother Rachel (Roza) Klein also had rabbinical lineage.
She was one of the daughters of Chaim (Jakob) Friedrich who was Rabbi of the Orthodox Community in Tur?, Satu Mare County, Romania.From early on in Ernest Klein's childhood, his greatness was already noted.
At the young age of nine years, Klein was able to recite the entire Book of Psalms by heart.
As a youth in Hungary, Klein spent his free time in between classes learning new languages.
Remarkably, at the age of 15, Klein taught himself English using English language textbooks.
Klein had a great talent in learning languages.
In an interview by The Canadian Jewish News (August 1, 1975), Klein recalls traveling from his birthplace Satu Mare, Romania to Austria, a little uneasy at the prospect of studying in a foreign country where he did not know the language.
Klein taught himself German during the few days journey, and by the end of the year he was the best pupil in his class.
Later, over the years Klein acquired knowledge and knew over 40 languages.
Klein studied languages, philology and exact philosophy in the University of Budapest and the University of Vienna; he received his Doctorate of Philosophy from the latter in 1925.
That year, he was deported to Auschwitz and later to the Dachau concentration camp, where he was liberated.
After the war he served as rabbi in Satu Mare.
After emigrating to France, he was a rabbi of the synagogue on Rue de Montevideo in Paris (1950–1951) and in 1952 he emigrated to Canada, where he held the post of Rabbi of Congregation Beth Yitshak in Toronto until his death.
He is the author of A Comprehensive Etymological Dictionary of the English Language (1966–1967).
He is also the author of A Comprehensive Etymological Dictionary of the Hebrew Language for Readers of English (1987), an English-language etymological dictionary of Hebrew to which he devoted the last ten years of his life.
In 1978, he was made an Officer of the Order of Canada.