Harry Potter author J K Rowling shared the inspiration for Snape's first name. 

One of the most controversial characters in the wizarding universe, it may seem like Professor Snape took great pleasure in humiliating Harry Potter whenever possible. His treatment of Harry, combined with many other acts of cruelty throughout the series, made it hard for some fans to see Snape as anything other than evil. However, the conclusion of the series shows Snape was at the very least brave and deeply loved Harry's mother. 

However, Rowling new reveal is far less mysterious. According to a tweet shared by the author, the name came from a street that she often passed on her way to work. Also, Rowling shared that she didn't realise why she chose Severus' name until she walked by the sign again.