According to E. De Felice, the surnames Bilardo, Vilardo and Vilardi form part of a broader set of variants such as Berardi, Verardi and Velardi, arisen from different personal names of Germanic origin that, over time, ended up converging and generating similar forms. In particular, he distinguishes two great lines: the one that derives from Berardo (composed of beran, "bear", and hardhu, "strong"), and the one that refers to Werhard (warja, "army", + hardhu), especially in the north. In the southern regions, where the oscillation between b and v is common, these forms underwent phonetic adaptations that gave rise to variants such as Bilardo, Velardi and Vilardi. In this way, surnames such as Vilardo or Vilardi can be interpreted as southern developments of these same bases.

On the other hand, E. Rossoni puts forward a more specific explanation for the forms Bilardo and Bilardi, linking them with the Germanic anthroponym Bilihard, formed by bili ("sweet, kind") and hard ("strong"), with an approximate sense of "firm but of a kind character". This author notes that these variants are documented in different regions, with a presence in Liguria, Lazio and above all in Sicily, while Vilardo and Vilardi appear more strongly in western Sicily, Calabria and the Naples area. From this perspective, the forms in Vil- can be understood both as a result of the phonetic passage from b to v characteristic of southern Italy, and also by the influence and overlap with other variants of the same group, which explains the complexity and diversity of this set of surnames.