nickname

A familiar, invented name for a person or thing used instead of the actual name of the person or thing, often based on some noteworthy characteristic.

"The Big Apple" is a common nickname for New York City.

[…] Plato, who was named Aristocles after his grandfather, but received from his gymnastic master the nickname Πλάτων (from πλάτυς, broad), which practically superseded his real name.

A familiar, shortened or diminutive name for a person or thing.

My name is Jonathan, but I go by my nickname, Johnny.

To give a nickname to (a person or thing).

Gerald, nicknamed "Jerry", was usually a very cheerful person.

He was nicknamed Chemical Ali by Iraqi Kurds, who also called him the Butcher of Kurdistan