Charles Ellicott Commentary Jeremiah 50:31

"Behold, I am against thee, O thou proud one, saith the Lord, Jehovah of hosts; for thy day is come, the time that I will visit thee." — Jeremiah 50:31 (ASV)

O thou most proud. —Literally, O Pride, the prophet using the word (Zadon) as a proper name for Babylon, as he had before used Merathaim and Pekod (Jeremiah 50:21). It is analogous in its meaning to the Rahab of Isaiah 51:9; Psalms 87:4; Psalms 89:10, as the name of Egypt. The word points, perhaps, to the self-exaltation of Nebuchadnezzar as embodying that of his people (Daniel 4:30).