'demagnetisation' originates from Modern English, specifically formed from the prefix 'de-' (from Latin 'de-' meaning 'remove' or 'reverse'), the base 'magnet' (from Latin 'magnes', from Greek 'magnētis' meaning 'Magnesian stone'), and the noun-forming suffix '-isation' (from French '-isation').

'demagnetisation' developed from the verb 'demagnetize' (itself formed by combining 'de-' + 'magnetize') with the addition of the noun suffix '-ation'/'-isation' to denote the action or process; 'magnet' traces back via Latin 'magnes' to Greek 'magnētis'.

Initially it meant 'the action of removing magnetism', and over time it has retained this technical meaning as the standard sense of the word.