Transistor

1) A transistor is a small electronic part in something such as a television or radio, which controls the flow of electricity.
2) A transistor or a transistor radio is a small portable radio.
Transistor is a tiny electrical device that can amplify an electrical signal and switch a device on and off.

A semiconductor device, having three or more terminals attached to electrode regions, in which current flowing between two electrodes is controlled by a voltage or current applied to one or more specified electrodes. The device is capable of amplification, etc, and has replaced the valve in most circuits since it is much smaller, more robust, and works at a much lower voltage See also junction transistor, field-effect transistor.

Sources:

Collins English Dictionary “Repagination”, 2018 https://www.collinsdictionary.com/dictionary/english/repagination

Nick Brieger, Alison Pohl: Technical English Vocabulary and Grammar.