'realness' originates from Late Middle English, combining the adjective 'real' (originating ultimately from Latin 'realis') and the suffix '-ness' from Old English.

'realness' appeared in Middle English as 'realnesse' (or similar spellings) formed by adding Old English-derived suffix '-nesse' to 'real'; over time the spelling and pronunciation regularized into modern English 'realness'.

Initially it simply denoted the state or quality of being 'real' (i.e., 'having reality'); over time it has retained that core meaning while also coming to be used for nuances such as authenticity or perceived reality in cultural and philosophical contexts.