'devilishness' originates from Old English/Germanic roots and Latin influence, specifically the Old English word 'deofol' (from Latin 'diabolus'), where 'deofol/diabolus' meant 'devil', combined with the adjective-forming suffix '-ish' and the noun-forming suffix '-ness'.

'devilishness' changed from Middle English forms such as 'devilishe'/'devilish' and eventually became the modern English word 'devilishness' through the addition of the suffix '-ness'.

Initially it meant 'having the qualities of a devil' (i.e., extreme wickedness or evil), but over time it also came to be used for 'mischievous, impish behavior' as well as for outright wickedness.