Both E. De Felice and E. Rossoni connect this surname to the place name Morra De Sanctis — historically known as Morra Irpino, located in the area of Avellino, in Campania. De Felice holds that the surname derives directly from that place name and from its corresponding demonym.

Rossoni broadens the picture considerably. He proposes that the surname may derive from several localities whose names trace back to the Germanic word mōra, meaning "marsh" or "waterlogged ground." Among the place names he cites are Morra del Villar and Morra San Giovanni, in addition to Morra Irpino. Rossoni also notes that a derivation from nicknames connected to a fondness for the game of morra cannot be ruled out.

On geographic distribution, Rossoni observes that the surname has independent origins in different regions of Italy. The northern group, concentrated in the areas of Turin, Asti and Cuneo, would derive from local Piedmontese place names, while the central-southern group — present in areas such as Rome, Frosinone, Caserta, Naples, Salerno, Avellino, Foggia and Bari — would be linked to the place name Morra Irpino.

It is also recorded as a locative surname derived from Morra De Sanctis, identified broadly as a locality near Naples.