A derecho (pronounced similar to "deh-REY-cho" in English) is a widespread and long lived windstorm that is associated with a band of rapidly moving showers or thunderstorms.
The word "derecho" was coined by Dr. Gustavus Hinrichs, a physics professor at the University of Iowa, in a paper published in the American Meteorological Journal in 1888. A defining excerpt from this paper can be seen by clicking here. Dr. Hinrichs chose this terminology for thunderstorm induced straight-line winds as an analog to the word tornado. Derecho is a Spanish word which can be defined as "direct" or "straight ahead" while tornado is thought by some, including Dr. Hinrichs, to have been derived from the Spanish word "tornar" which means "to turn".
By definition winds in a derecho must meet the National Weather Service criterion for severe wind gusts (greater than 57 mph) at most points along the derecho path. In the stronger derecho events winds can exceed 100 mph. For example, as a derecho roared through northern Wisconsin on July 4, 1977, winds of 115 mph were measured. More recently, the derecho which swept across Wisconsin and Lower Michigan during the early morning hours of May 31, 1998 produced a measured wind gust of 128 mph in eastern Wisconsin and estimated gusts up to 130 mph in Lower Michigan.