The word 致命 is formed by combining the character 致, which means "to cause" or "to deliver", with the character 命, which means "life". It constructs its meaning through a direct, cause-and-effect logic: the first character acts upon the second, so the compound literally reads as "to cause life" but is conceptually understood in reverse as "causing (the loss of) life", thus arriving at its meaning of "fatal" or "deadly".