'normal-length' originates from the combination of 'normal' and 'length', where 'normal' meant 'conforming to a standard' and 'length' referred to 'the measurement of something from end to end'.

'normal' and 'length' have been used in English since the Middle Ages, and their combination into 'normal-length' is a modern construct to describe standard measurements.

Initially, 'normal' and 'length' were used separately, but over time they combined to describe something of standard measurement.