1. A device, such as a variable capacitor or inductor, that is used to alter the resonant frequency of a tuned circuit.

2. The first stage of a radio or television receiver that is used to select a particular broadcast channel. It contains either a tuned circuit in which the resonant frequency may be altered to accept the desired channel frequency or a set of resonant circuits each of which is tuned to an individual channel and may be selected (see turret tuner).