'banefulness' originates from English, built from the adjective 'baneful' + the noun-forming suffix '-ness'; 'baneful' itself comes from 'bane' + '-ful', where 'bane' originally meant 'slayer' or 'cause of death' in Old English.

'bane' came from Old English 'bana' (meaning 'slayer'), which developed into Middle English 'bane'; from this arose the adjective 'baneful' and then the noun 'banefulness' (earlier Middle English forms include 'banefulnesse').

Initially, the root 'bane' meant 'slayer' or literal 'cause of death'; over time its sense broadened to mean any source of harm, and 'banefulness' now denotes the quality of causing harm or ruin.