'semitone' originates from Latin, specifically the word 'semitonium,' where 'semi-' meant 'half' and 'tonus' meant 'tone.'

'semitonium' transformed into the Old French word 'semiton,' and eventually became the modern English word 'semitone' through Middle English.

Initially, it meant 'half of a tone,' and this meaning has largely remained the same in modern usage.