Some big investor made a $5.13 million options bet Thursday that April could be a cruel month for stocks.
A sizable trade in VIX options caught the eye of traders, who say it's one of the first big bullish trades on the Volatility Index for April and assumes a 50 percent jump in the index.
The VIX, the Chicago Board of Options Exchange's Volatility Index, is viewed as a fear gauge for the stock market. It estimates expected volatility by averaging weighted prices of puts and calls over a range of strike prices. A high VIX is viewed as bearish for stocks.
(Read more: Nervous investors need to embrace the selloff)