'eeriness' originates from English, specifically formed from the adjective 'eerie' plus the noun-forming suffix '-ness', where '-ness' denoted 'state or quality'.

'eerie' changed from Scots dialect word 'eerie' (meaning 'fearful, uncanny') and was adopted into modern English; the noun 'eeriness' developed by combining 'eerie' with '-ness' to denote the state or quality.

Initially related to 'fearful' or 'timid' senses in older dialects, the sense shifted to the modern meaning emphasizing 'uncanny' or 'strangely frightening'; 'eeriness' now specifically denotes the quality of being eerie.