E. Rossoni traces the surname to medieval Germanic personal names that entered northern Italy during the Lombard period and subsequently spread through Franco-Occitan influence on Liguria and Piedmont. The name is built from two Germanic elements: *aig- or *agi-, meaning "one's own" or "valour," and *hardhu-, meaning "strong, brave, bold" — the latter cognate with German hart and English hard. Medieval Latin documents of the eleventh and twelfth centuries record the forms Aicardus, Agicardus, and Achardus. The combined meaning points to something like "he who is distinguished by his own character and strength."

Rossoni identifies Icardi as a dialectal variant of Aicardi, representing a northward shift from Liguria into Piedmont, particularly into the areas of Turin and Alessandria. He also notes that the form may alternatively derive from aphaeresis — that is, the dropping of the initial syllable — of the name Riccardi. It is similarly recorded that the surname is typical of the provinces of Alessandria and Turin, and that the base name Aicardo is already documented as early as the ninth century in the Latinized forms Agicardus and Aicardus, ultimately from the Gothic name Aichar, carrying the senses of "characteristic, original" and "strong, courageous, daring."