Kill-crazy is a term used to describe someone who seems to have an unnatural and excessive desire to kill others. While it may not always be easy to find a direct synonym, there are many phrases and words that can convey a similar meaning. Some possibilities include "bloodthirsty," "murderous," "heinous," "violent," "ruthless," "savage," "merciless," "cruel," and "brutal." Each of these conveys a strong sense of disregard for human life and a willingness to commit violent acts without concern for the consequences. While the term "kill-crazy" may be uncommon, there are many ways to convey a similar idea through language.