The authors agree that this surname is of Germanic origin and is linked to the name Gertrudis, whose meaning is articulated in two components. A. Bongioanni notes that the first element may be agil or ag —related to the Latin acies and acutus, with the sense of "point" or "sword"— or else gar / ger, meaning "spear"; the second element, trut / treu, means "faithful". V. Blunda, for his part, analyses it as a compound of gaira ("spear") and druda ("faithful", "beloved"), with the overall sense of "faithful spear" or "beloved spear", and notes that this combination reflects a Germanic conception that linked warrior strength with the bonds of loyal affection within the lineage.

Bongioanni indicates that the name gave rise to various forms in Italy, among them Agiltruda and Aldruda —the latter of Tuscan use—, and that the Piedmontese surname derived is Astrúa, with forms documented in Piacenza from the year 716 and in Saluzzo and Vercelli from the 13th century. He adds that Strolengo, also Piedmontese, is possibly a patronymic of the same name. Blunda, on the other hand, focuses his analysis on Sicily and mentions as a hagiographic reference Saint Gertrude the Great (1256–1302), a Cistercian nun of Saxony and a central figure of medieval mysticism.