The surname has multiple independent ancestral stocks (ceppi), arising in different regions with no direct connection between them. F. De Laurentiis notes that its diffusion is concentrated mainly in two distant and autonomous areas: Tuscany and northeastern Italy on the one hand, and the peninsular south on the other.

For Tuscany, E. De Felice proposes that the surname reflects a hypocoristic by aphaeresis of Ademaro or Adimaro, citing as documentary evidence the Libro di Montaperti of Florence (1260): Adimari qui Mari dicitur. E. Rossoni concurs, pointing to names such as Valdemaro or Ademaro as the most likely origin. For the south, De Felice adds that the surname may derive from a hypocoristic of Amari, or alternatively from a nickname based on the southern adjectives amaro, amaru, or maru, carrying the figurative sense of "unfortunate, unhappy." De Laurentiis records the same hypotheses. All the scholars cited here also mention the given name Mario as a possible base.

V. Blunda offers a distinct perspective for the Sicilian context: he traces the surname to the Germanic personal name Maru, linked to the root maru with the meaning of "famous, renowned, illustrious," which functions as the second element in compound names such as Adimaro, Otomaro, or Volkmar. Blunda further cautions that the popular association with the Italian noun mare ("sea," from the Latin mare) constitutes a false etymology, unrelated to the Germanic anthroponym.

It is also recorded that the surname may represent an aphetic form of Altimari.