Earpiece (noun)

1. A device, typically part of a headset, that fits into the ear and transmits sound.
2. A small device that is worn in or attached to the ear and used to listen to sound.

Origin:

Late 19th century: from ear + piece.

Examples:

1. She put on the earpiece and listened to the audio tour of the museum.
2. The security guard wore an earpiece to receive instructions from headquarters.
3. The earpiece of the phone was damaged, causing poor sound quality.
4. The earpiece of the hearing aid was custom fit to the patient's ear.
5. The earpiece of the headset was comfortable and allowed for hands-free phone conversations.