The authors agree that this surname derives from the medieval name Lapo (also documented in Latin as Lapus), itself a hypocoristic contraction of Iacopo (Iacopus), the Italian form of the name Jacob, already frequent from the 12th century.

E. De Felice notes that the surname is frequent in Tuscany. E. Rossoni specifies that it is a typically Tuscan surname, with a particular hold in the Florence area, and supplies historical documentation: the form Lapus appears in a deed of the second half of the 13th century, while in the 17th century a certain "Ser Giovanni Lapi, notary of the merchandise" is recorded in Florence.

Rossoni also documents related surnames: Lapini, likewise Tuscan, present in the Florence, Arezzo, Pistoia and Siena areas; Lapucci, typical of Florence and Pisa; and Lapponi, with a presence in areas of Macerata and Rome.