E. De Stefani notes that this surname originates in the given name Jan, a form of Germanophone and Slavic tradition derived from the Latin Johannes, itself of Hebrew root with the meaning "God gives" or "God has mercy". In time, that name became a surname. De Stefani considers it likely that it reached Carinthia from Slovenia —historical Carniola— and that in the 18th century it settled in Carnia, the mountainous area of northern Friuli-Venezia Giulia, in the province of Udine. In Carinthia, related forms such as Jannach, Janisch, Jannasch and Janesch are attested; in Slovenia, the form Janič appears especially in Ljubljana and in the border area with Italy.

E. Rossoni places the surname as proper to the Udine area and adds that the family would have originated in Poland, engaged in the glass trade, before moving to Austria. Around 1750, a member of the family married in Preone, in the province of Udine, and from that point various branches developed in Friuli-Venezia Giulia and in other Italian cities.