A phrase sometimes used to signify tranquility, or calmness; that is, the condition of one who has the calm and undisturbed use of his reason. In cases of homicide, it frequently becomes necessary to. ascertain whether the act of the person killing was done in cool blood or not, in order to ascertain the degree of his guilt. In the law of homicide. Calmness or tranquillity; the undisturbed possession of one’s faculties and reason; the absence of violent passion, fury, or uncontrollable excitement