'one-tone' originates from English, specifically a compound of the words 'one' and 'tone', where 'one' meant the numeral for a single unit and 'tone' referred to a musical pitch or quality of sound.

'one' comes from Old English 'ān' (meaning 'one, single'), while 'tone' derives ultimately from Greek 'tonos' via Latin and Old French forms (e.g. French 'ton'); the compound 'one-tone' is a modern English compounding of these elements.

Initially a literal compound meaning 'a single tone' in sound or pitch; over time it has also been used figuratively to describe speech or expression that is monotonous.