Albert Barnes Commentary Jeremiah 50:21

"Go up against the land of Merathaim, even against it, and against the inhabitants of Pekod: slay and utterly destroy after them, saith Jehovah, and do according to all that I have commanded thee." — Jeremiah 50:21 (ASV)

The land of Merathaim - of double rebellion. Like Mitsraim, that is, the two Egypts, Aram-Naharaim, that is, Syria of the two rivers, or Mesopotamia, it is a dual. It may have been a real name; or - the dual ending being intensive - it may mean the land of very great rebelliousness.

Pekod - Possibly a Babylonian town.

Waste - Rather, slay, (Jeremiah 50:27).