Wiktionary
n. (cx medicine English) Any unanticipated or unusual event in a medical setting which results in death or serious physical injury to a person or persons, specifically including limb loss or gross motor function.
Wikipedia
A Sentinel Event is defined by The Joint Commission (TJC) as any unanticipated event in a healthcare setting resulting in death or serious physical or psychological injury to a patient or patients, not related to the natural course of the patient's illness. Sentinel events specifically include loss of a limb or gross motor function, and any event for which a recurrence would carry a risk of a serious adverse outcome. Sentinel events are identified under TJC accreditation policies to help aid in root cause analysis and to assist in development of preventative measures. The Joint Commission tracks events in a database to ensure events are adequately analyzed and undesirable trends or decreases in performance are caught early and mitigated.