Definition of the word crack up

The origin of the phrase "crack up" in modern-day English can be traced back to the early 20th century. At that time, "crack" was a term used in horse racing to describe a horse's strong and sudden acceleration. This usage was inspired by the sound of a horse's bones cracking as it broke into a gallop. In the 1920s, "crack" began to be used in other contexts, particularly in slang related to criminal activities, such as stealing a safe or escaping from prison. It soon came to be used more generally as a term for anything that happened suddenly and unexpectedly, such as a joke or humorous situation that caused laughter. The phrase "crack up" entered the vernacular in the 1940s and 50s, and it came to be used primarily to describe someone laughing or finding something humorous to an extreme point. It can imply a sense of hysteria or losing control due to intense laughter. Overall, the origin of "crack up" is a result of the evolution of the word "crack" from its racing origins, and its adaptation and usage in different contexts over time.