'barbariousness' originates from English, specifically formed from the adjective 'barbarious' plus the suffix '-ness', where 'barbarious' ultimately derives from Latin 'barbarīus' (from Greek 'barbaros') meaning 'foreign, strange'.

'barbarious' was influenced by Latin 'barbarīus' and Old French forms related to 'barbarous'; Middle English used forms like 'barbarous' and later English formed 'barbarious' and then the noun 'barbariousness'.

Initially associated with the idea of 'foreignness' or 'strangeness' (from Greek/Latin), it shifted toward the sense of 'uncivilized' or 'savage' and that evolved into the modern meaning of 'cruel or uncivilized behavior'.