According to E. De Felice, the surnames of the group Bilardo, Vilardo and Vilardi should be interpreted within a broader system of forms such as Berardi, Verardi, Velardi, originating in the transformation into a surname of various Germanic personal names which, over time, crossed and became confused with each other. In this sense, he identifies at least two major lines: on the one hand, the Berardi type, derived from Berardo (from beran, "bear", and hardhu, "strong"), and on the other the Verardi type, which in the north continues the Alemannic name Werhard (warja, "army", + hardhu). In southern Italy, where the alternation between b and v is frequent, these forms undergo phonetic adaptations that give rise to variants such as Velardi or Vilardi, so that surnames such as Vilardo or Vilardi can be, in many cases, southern developments of these same bases.

For his part, E. Rossoni also proposes a specific derivation for the forms Bilardo and Bilardi, linking them with the Germanic name Bilihard (from bili, "sweet, kind", and hard, "strong"), meaning "of sweetly firm character". This author highlights the presence of Bilardo and Bilardi in areas such as Liguria, Lazio and especially Sicily, while Vilardo and Vilardi present important clusters in Sicily (Palermo, Trapani), Calabria and the Neapolitan area. From this perspective, the forms in Vil- can be explained both as a phonetic evolution of Bil- (through the shift from b to v typical of the south) and by the confluence with other series such as Verardi, which reinforces the idea of a group of surnames where different Germanic roots ended up overlapping in the Italian tradition.