Sobriquet

A sobriquet (/ˈsoʊbrᵻkeɪ/ SOH-bri-kay) is a nickname, sometimes assumed, but often given by another. Distinct from a pseudonym that is assumed as a disguise, it usually is a familiar name, familiar enough such that it may be used in place of a real name without the need of explanation. This salient characteristic is of sufficient familiarity that the sobriquet may become more familiar than the original name.

Examples are Emiye Menelik, a nickname of Emperor Menelik II of Ethiopia, who was popularly and affectionately recognized for his kindness ('emiye' means mother in Amharic); Genghis Khan, who now is rarely recognized by his original name, Temüjin; and Mohandas Gandhi, who is better known as Mahatma Gandhi. Well-known places often have sobriquets, such as New York City, often referred to as the Big Apple. Therefore, sobriquet may apply to the nickname for a specific person, group of people, or place.

Two early variants of the term are found, sotbriquet and soubriquet; often, the latter form is still used. The modern French spelling is sobriquet. The first form suggests derivation from sot, foolish, and the second form, briquet, is a French adaptation of Italian brichetto, diminutive of bricco, ass, knave, possibly connected with briccone, rogue, which is supposed to be a derivative of the German brechen, to break; but Skeat considers this spelling to be an example of false etymology. The real origin is to be sought in the form soubriquet.

...
Wikipedia