Cynefin is a Welsh word meaning habitat, in the sense used in the biological sciences: a place where many things live. It is a framework for understanding why some incidents and problems are so difficult to resolve. The author of the Cynefin model is Dave Snowden: his excellent talks introducing the Cynefin framework can be found on YouTube.
Part of the beauty of the framework is the simplicity of drawing four lines and building the story in the five areas that creates.
In problem solving, I link the Cynefin framework with the ITIL concepts of incident management and problem management. There is a natural synergy between the two framework. Together the Cynefin & ITIL frameworks can be used to explain why some adverse events keep recuring and why some problems are not being resolved by an in-house team.
Foot Note: If you're not going to treat the Cynefin framework seriously because Cynefin is not an English word, then that is like a medical doctor not treating a patient with Kawasaki disease because Kawasaki is not an English word.