'unwarrantedness' originates from English, specifically from the adjective 'unwarranted' (un- + 'warrant'), where 'un-' is a negation prefix meaning 'not' and 'warrant' ultimately comes from Old North French 'warant' meaning 'to guarantee or protect'.

'warrant' came into English from Old North French 'warant' (also seen as 'garant' in some dialects), later forming the adjective 'warranted' and then 'unwarranted'; the abstract noun was formed by adding the noun-forming suffix '-ness' to produce 'unwarrantedness'.

Initially related to lack of guarantee or protection, the sense shifted toward lacking justification or lawful authority; today it is used to mean 'without proper reason or justification'.