Psychology is the scientific study of mind and behavior. (of an illness or other physical problem) caused by…. [1][2] its subject matter includes the behavior of humans and nonhumans, both conscious and unconscious phenomena, and mental processes such as thoughts, feelings, and motives. See examples of psychological used in a sentence. · psychology, scientific discipline that studies mental states and processes and behaviour in humans and other animals. Relating to the human mind and feelings: Of or relating to psychology. A large profession of practitioners and a smaller but growing science of mind, brain, and social behaviour. The meaning of psychological is of or relating to psychology. How to use psychological in a sentence. The discipline of psychology is broadly divisible into two parts: