The term 'ONE OF TWO IN AN ENGLISH HORN' can be summarized by the crossword solution 'REED'. A REED is a thin strip of material, usually made of wood or metal, that vibrates to produce sound when air is blown through it. In an English horn, two reeds are used to create a unique sound. The reeds are placed in the mouthpiece of the instrument and vibrate when air is blown through them. This vibration creates the sound of the English horn.