sudden death; unexpected death
Medical and general term for death that occurs suddenly and unexpectedly, often from natural causes like heart attack or stroke. Also used in non-medical contexts for any abrupt, unforeseen death.
He died of sudden death.
An autopsy was performed to investigate the cause of the sudden death.
突然死 is the clinical/medical term for sudden death, while 急死 is the everyday word used in news and conversation.
Compound of 突然 (sudden) and 死 (death). The exact historical derivation is uncertain, but the term is a straightforward Sino-Japanese compound.