'loquaciousness' originates from Latin, specifically the word 'loquācus' (from 'loquāx'), where 'loqu-' meant 'to speak', and it also includes the English noun-forming suffix '-ness' ultimately from Old English 'nes(s)e' meaning 'state or quality'.

'loquācus' in Latin developed into Late Latin forms such as 'loquāc(i)ōsus' and was borrowed into English as 'loquacious' in Middle English; the modern noun 'loquaciousness' was formed in English by adding the suffix '-ness' to 'loquacious'.

Initially it described being 'given to speaking' or 'talkative'; over time it came to be used as a noun meaning 'the quality or state of being talkative'.