It may seem ludicrous to define a sensation that most everyone has experienced (except, for example, people born with complete insensitivity to pain). One standard reference work defines pain as a "more or less localized sensation of discomfort, distress, or agony, resulting from the stimulation of specialized nerve endings."
PAIN
Meaning of PAIN in English
English dictionary of medicine. Английский словарь медицины. 2012