great shock; major shock
Used to describe a very surprising or upsetting event, stronger than ショック alone. Common in casual conversation and news.
彼の突然の辞職は大ショックだった。
His sudden resignation was a great shock.
そのニュースを聞いて大ショックを受けた。
I was greatly shocked to hear the news.
Compound of 大 (dai, 'great') and ショック (shokku, from English 'shock').