Gnaeus Cornelius Cossus was a consular tribune in 414 BC and consul in 409 BC of the Roman Republic. Cornelius belonged to the Cornelia gens, one of the older patrician gentes of the Republic. Cornelius' father was the Roman hero Aulus Cornelius Cossus who had slain the King of the Veii, Lars Tolumnius, in single combat. Cornelius had two known brothers, , consul in 413 BC and Publius Cornelius Cossus, consular tribune in 408 BC. There are no known children of Cornelius.