'single-wavelength' originates from the combination of 'single' and 'wavelength', where 'single' means 'one' and 'wavelength' refers to the distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave.

The term 'wavelength' was first used in the 19th century to describe the distance between wave crests, and 'single' has been used since Old English to denote 'one'.

Initially, 'wavelength' referred to the physical distance in waves, and 'single' meant 'one'. The combined term 'single-wavelength' has maintained its meaning of 'one wavelength' in modern usage.