Genesis 1:2 (NASB): "The earth was formless and void, and darkness was over the surface of the deep, and the Spirit of God was moving over the surface of the waters."
The Hebrew term that is rendered "the deep" is תְּהוֹם (tehom), which is also translated "the great deep" in Gen. 7:11 (KJV) since it's coupled with the adjective רָב. Theologians/Bible scholars often interpret Gen 1:1-2 as a polemical answer to the Babylonian myth of Tiamat and Marduk. Gerhard von Rad apparently buys into this idea too. However, the Babylonian narrative is set within a polytheistic context unlike Genesis. But even more devastating to the Tiamat theory is the linguistic evidence against it.
For instance, scholar Victor Hamilton interacts with the claims regarding tehom and Tiamat, and I believe he shows it's uncertain that these words are cognate. In fact, there are reasons to believe otherwise. From what I've read, Mitchell Dahood (a late and esteemed philologist) seriously questioned the supposed linguistic connection between tehom and Tiamat.
For Dahood's exact quote, see https://books.google.com/books?id=lotBnvqdmeQC&pg=PA96&dq=dahood+tehom&hl=en&sa=X&ved=0ahUKEwiJ566Ks6LVAhWJdSYKHcW9AjQQ6AEIQzAF#v=onepage&q=dahood%20tehom&f=false
It is page 96, footnote 34. Dahood spoke of the "unsustainable connection" between these words. So the objections I've found to associating tehom with Tiamat seem devastating.
Dahood writes that the linguistic correspondence between tehom and thm (Ugaritic) is "much more likely" than a connection between tehom/Tiamat. Yet the Akkadian term related to tehom is also evidently cognate. According to biblehub, there are 36 occurrences of tehom in the Hebrew Bible, I think.
For now, I reject the Tiamat connection (linguistic association) with tehom; there is too much evidence against it. The myth that Tiamat is cognate with tehom began spreading after Hermann Gunkel (a German OT scholar) began to perpetuate the idea. Linguistically, it is nigh impossible to prove: weigh the evidence and arguments carefully, then you decide.