My iMac keeps crashing
I think this is a CPU power transistor failure. After doing some research, I noticed that 2013-2015 Macbooks had a similar issue. The transistors that switch the CPU from high to low power are too slow in heat and don't switch fast enough, causing a crash. The solution that fixed it for me was to install Macs Fan Control and set this rule: 
This seemed to fix the issue for me. As happened to you, random processes, such as Word and kernel_task were being named the culprit.