'anonymousness' originates from English, specifically formed from the adjective 'anonymous' plus the suffix '-ness'; 'anonymous' ultimately comes from Greek 'ἀνώνυμος' ('anōnumos'), where the prefix 'a-' meant 'not' and 'onoma' meant 'name'.

'anonymous' changed from Greek 'anōnumos' into Latin/Medieval Latin forms and then into Middle English 'anonymous'; the modern English noun 'anonymousness' was later formed by adding the Old English-derived suffix '-ness'.

Initially it meant 'without a name', but over time it evolved into the current sense of 'the state of being unnamed or unidentifiable; lacking an identifiable name or identity'.