The only free and comprehensive online etymological dictionary of the Spanish language
justo (Adjective) "just," "fair"
12th cent. From Latin iustus 'id.' From Proto-Italic *jowes-to- 'id.' Potentially a somewhat late adjective derived from *jowes- "oath." For a continued etymology, see jurar.
The word is the origin of a number of surnames, Justo, Justa, Justal, Juste, Justos, Justes. Also the origin of Justel, a small village in Leon.
Asturian xustu, Portuguese justo, Galician xusto, Catalan just, French juste, Italian giusto, Aromanian giustu, Romanian just, Sardinian giustu