mid-14c., representing the Greek rendition of Akkadian Bab-ilani "the gate of the gods," from bab "gate" + ilani, plural of ilu "god" (compare Babel). The Old Persian form, Babiru-, shows characteristic transformation of -l- to -r- in words assimilated from Semitic. Formerly also applied by Protestants to the Church in Rome, from the woman "arrayed in purple and scarlet" in Revelation xvii.5 ("And upon her forehead was a name written, Mystery, Babylon the Great, the mother of harlots and abominations of the earth").
variant of suffix -an (q.v.), with connective -i-. From Latin -ianus, in which the -i- originally was from the stem of the word being attached but later came to be felt as connective. In Middle English frequently it was -ien, via French.
<a href="https://www.etymonline.com/word/Babylonian">Etymology of Babylonian by etymonline</a>
Harper, D. (n.d.). Etymology of Babylonian. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/Babylonian