'silencio' originates from Latin, specifically the word 'silentium', where the root 'silēre' meant 'to be silent'.

'silentium' passed into Vulgar Latin and Old Spanish as forms that eventually became modern Spanish 'silencio' (also related to Old French 'silence' and Late Latin usage).

Initially, it meant 'the condition of being silent' (from Latin) and over time has retained that core meaning while also being used for specific kinds of imposed or respectful silence.