What is "cniva"

Cniva (from kniwa, meaning "knife"; mid-3rd century AD) was a Gothic chieftain who invaded the Roman Empire. He successfully captured the city of Philippopolis ( Plovdiv in Bulgaria) in 250 and killed Emperor Decius and his son Herennius Etruscus at the battle of Abrittus as he was attempting to leave the Empire in 251. This was the first time a Roman Emperor had been killed in combat against barbarians. He was allowed to leave with his spoils and was paid tribute to stay out of the empire.