'antimusicalness' originates from the combination of 'anti-' (from Greek 'anti', meaning 'against'), 'musical' (from Latin 'musicus', ultimately from Greek 'mousikos', meaning 'of the Muses'), and the English suffix '-ness' (from Old English 'nes(s)', forming abstract nouns).

'antimusicalness' was formed in modern English by affixing the prefix 'anti-' to the adjective 'musical' and adding the nominalizing suffix '-ness'. 'Musical' itself evolved from Latin 'musicus' via Old French/Medieval Latin, which in turn comes from Greek 'mousikos'.

Originally Greek 'mousikos' meant 'of the Muses' (relating to the Muses and their arts); over time this developed into 'relating to music' in Latin and Old French. The addition of 'anti-' created a sense of 'against music' and the suffix '-ness' converted that into 'the state or quality of being against music' (i.e., 'antimusicalness').