The term PSYCHOLOGIST'S 'I' is represented by the crossword solution EGO, which is a three letter word. EGO is a term used in psychology to refer to the conscious self-awareness of an individual's identity and their sense of self. It is often used to describe the part of the psyche that mediates between the conscious and unconscious mind. EGO is also used to refer to the sense of self-importance and self-esteem that an individual has.