V. Blunda describes this surname as of Germanic origin, derived from the personal name Ernst, linked to the root ernust, with the sense of "seriousness, gravity, firmness of purpose". That root is preserved without alteration in modern German with the same meaning. Blunda notes that, in Germanic anthroponymy, firmness of character was a quality valued as a complement to warrior valour, and that the name spread through Central Europe through the Saxon and Habsburg dynasties, reaching Italy by way of dynastic marriages. He considers it a surname peculiar to Sicily.

A. Bongioanni agrees on the Germanic origin of the name, although he adds a different perspective on its etymology. He observes that the modern German form Ernst seems equivalent to the Latin Severus, but that the older form Arnust would derive, according to some authors, from the root ar, meaning "eagle", which would relate it to names such as Arnaldo or Arnolfo. Bongioanni also mentions that Saint Ernest is celebrated on 12 January.