1. the intellectual identification with or vicarious experiencing of the feelings, thoughts, or attitudes of another.
Identifying oneself completely with an object or person, sometimes even to the point of responding physically, as when, watching a baseball player swing at a pitch, one feels one's own muscles flex.
2 : the action of understanding, being aware of, being sensitive to, and vicariously experiencing the feelings, thoughts, and experience of another of either the past or present without having the feelings, thoughts, and experience fully communicated in an objectively explicit manner; also : the capacity for empathy
[Emphasis obviously mine]