Plump down and Place down

Plump down verb - Set (something or oneself) down with or as if with a noise.

Place down and plump down are semantically related. In some cases you can use "Place down" instead a verb "Plump down".

Place down verb - Cause to sit or seat or be in a settled position or place.

Plump down and place down are semantically related. Sometimes you can replace term "Plump down" with "Place down", this phrasal verbs are similar.