tuner

Short definition from Wiktionary

Noun

1. 1
   A person who tunes a piano or organ.
2. 2
   A device, electronic or mechanical, that helps a person tune a musical instrument by showing the deviation of the played pitch from the desired pitch.
3. 3
   On a musical instrument, a peg or mechanical device that changes the tension, and hence pitch, of a string.
4. 4
   The component of an audio system that receives radio broadcasts.
5. 5
   One who sings or makes music.
6. 6
   A musical.