Like most Yiddish expressions, this is Mediaeval Low German. In Modern German it would be spelled "Ach! Gewalt!" Gewalt is a word that means strength or force, But in this context means "violence".

I see others referring to the Yiddish expression "oy vay zmir". Again, in Modern German, "Ach! Weh ist mir!", literally, "oh, woe is unto me!" In all 3 cases, the pronoun is in the Dative case, which usage has long since vanished in English, except in antique sayings such as this.
by ProudPrimate July 10, 2013
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Yiddish phrase. exclamation of surprise, incredulity, or simply used to emphasize a statement. often used when kvetching. alt. spelling: oy gevaldt
oy gevalt! don't scare me like that.
oy gevalt, not again.
oy gevalt, that was a long drive!
by Shwaggy November 14, 2003
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A yiddish term meaning "Oh goodness!" An expression of utmost anxiety or shock.
"Oy Gevalt! Would you look at the tuchis on her!"
by Reb'Ke'ev March 17, 2005
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Oy, gevalt! I hear Sam Jones got a divorce and married his friend, David.
by Tippy Ray March 8, 2005
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"Oy vey zmir"... that doesnt say much either, but its a yiddish phrase, and you can not really translate yiddish to english. The best defintion would be "oh boy or oh my gosh!"
"Oy gevalt, im soo tired, i need to go to bed but i have too much homework."
by JBS May 7, 2003
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