'protractor' originates from Latin, specifically the word 'protrahere', where 'pro-' meant 'forward' and 'trahere' meant 'to draw'.

'protractor' changed from the Medieval Latin word 'protractor' (from Latin 'protrahere') and was adopted into English as an agent/form instrument noun with the suffix '-or', eventually becoming the modern English 'protractor'.

Initially, it meant 'one who or that which draws out or prolongs', but over time it evolved into its current primary meaning of 'an instrument for measuring angles' (and secondarily 'something that protracts, e.g., a muscle').