According to E. Rossoni, it derives from Balus, a contraction of Valentinus. The initial V in Slovene is frequently transformed into B.

B. Zuanella notes that according to onomastics scholars, this surname could derive from the hagionym Valentinus or, better, from the contracted form Valus (compare the Friulian surnames Valussi and Valusso present in Udine, Pagnacco, Tavagnacco, Moruzzo). This name of Friulian origin was transformed, in Slovene mouths, into the form Balus. In the dialect of the Natisone the V sometimes tends to become B: Vernasso/Bernas, Valentin/Balentin, Vidaci/Bidaci, Birma/Vierma (confirmation), Verin/Berin (a large pool of water in the rivers), Weis/Bajs (the colour white). In the parish books of San Leonardo it is not rare to find the Slovene surnames Velicogna and Veliszach transcribed as Belicogna and Beliszach.