"the gate of god." (See among others: Brown, Driver and Briggs, Hebrew and English Lexicon; Easton's Bible Dictionary; The Seventh-day Adventist Bible Dictionary.)
"The Babylonian name Babilu (Babel or Babylon) meant 'gate of god.' In ancient times the city gate was the place where official visitors conducted public business. The name Bab-ilu reflected the belief that Babylon was the place selected by the gods to meet with human beings, and the claim of Babylonian kings that the gods had commissioned them to rule the world" (The Seventh-day Adventist Encyclopedia, under the heading "Babylon, Symbolic").
"The oldest attested extrabiblical name is the Sumerian ká-dingir-ki (usually written kádingir-ra, 'gate of god')" (The International Standard Bible Encyclopedia, Revised; see also The Anchor Bible Dictionary).
The meaning of Babel was later changed to reflect confusion. The Hebrew root from the word balal means "to confound" and refers to the confusion at the Tower of Babel (Gen. 10:10; 11:19). It comes to us today with this connotation, but we must remember its etymological religious root: "the gate of god." Putting the two thoughts together we get our understanding today that the metaphor of Babylon means ecclesiastical confusion in these last days.
The second angel's message was first given in the time frame and context
of the first apartment ministry of Jesus in the heavenly sanctuary.
Babylon is the metaphor which God gave John in order to illustrate the
antichrist power in the last days. The resistance of Babylon of old to
the gospel of God in the Old Testament typifies the antagonism of
spiritual Babylon in the Revelation.
--The two Babylons ultimately
represent spiritualism in the earth 
controlled by the enemy of the
gospel of God.
The fall of Babylon is the falling away from the everlasting gospel of
Christ crucified as preached during the time of God's judgment hour (Rev.
14:6-7).
God does not abandon in her guilt, but warns her of her
fallen condition (vs. 8). The fall here is not the image of merely
falling, but rather it suggests lying prostrate after a fall rather than
the fall itself.
Later in Revelation 18:2 the message of the fall of Babylon is repeated,
but it is presented with an additional message giving information that
Babylon at that time not only rejects the threefold message of
Revelation 14:6-7, "the everlasting gospel," but that she becomes
completely possessed and inhabited by demons as the result of that
rejection.
As a result of seeking to please sinners, the church becomes corrupt. Therefore, in Revelation 17, we see a church that holds a beautiful, golden cup, of which she makes all nations drink. What is in it? “Abominations and filthiness of her fornication.” Rev. 17:4"
Finneman