Plug-in and Voltaic

Plug-in noun - A printed circuit that can be inserted into expansion slots in a computer to increase the computer's capabilities.

Voltaic and plug-in are semantically related. In some cases you can use "Voltaic" instead an adjective phrase "Plug-in".

Voltaic noun - A group of Niger-Congo languages spoken primarily in southeastern Mali and northern Ghana.

Plug-in and voltaic are semantically related. Sometimes you can use "Plug-in" instead an adjective "Voltaic".