Plug in and Train of thought

Plug in verb - Plug into an outlet.

Train of thought and plug in are semantically related. In some cases you can use "Train of thought" instead a noun "Plug in".

Train of thought noun - The connections that link the various parts of an event or argument together.

Plug in and train of thought are semantically related. Sometimes you can use "Plug in" instead a noun phrase "Train of thought".