IPA: /ˈtjuːnər/
KK: /ˈtunɚ/
A device or person that adjusts or sets the frequency of a radio or musical instrument to ensure it produces the correct sound or signal.
The tuner helped me adjust my guitar to the right pitch before the concert.
Tuner → It is formed from "tune" (from Old French *ton*, meaning a musical sound or melody) and "-er" (meaning a person who). A tuner is a person who adjusts or sets the musical sound or melody.
Think of someone who adjusts or sets a musical sound — that's what a tuner does.