Imperial Aramaic

Short definition from Wiktionary

Proper noun

1. 1
   The chronolect of the Aramaic language (mid-8th century–late 4th century BCE), intermediate between Old Aramaic and Middle Aramaic, that was used as a language of public life and administration in the late Neo-Assyrian Empire (from the reign of King Tiglath-Pileser III [r. 745–727 BCE] onward), the Neo-Babylonian Empire, and the Achaemenid Empire, until the latter’s conquest by Alexander the Great
2. 2
   The Imperial Aramaic of the Achaemenid Empire (550–330 BCE) only.