So-and-so and Thingummy

So-and-so noun - A person whose behavior is offensive to others.

Thingummy and so-and-so are semantically related. In some cases you can use "Thingummy" instead a noun phrase "So-and-so".

Thingummy noun - A small article the actual name of which one either does not know or cannot remember.

So-and-so and thingummy are semantically related. Sometimes you can use "So-and-so" instead a noun "Thingummy".