The “Nephilim” are referred to in Genesis 6:4. These were two different groups on the earth before the flood. “Nephalim” is a precarious word simply because it is seldom used. Therefore it is not possible to translate the word with absolute certainty. It appears to be related to the Hebrew word “naphal” which is clearly translated as “fall.” As such, the word may carry with it a semantic nuance of “violent death”–as someone falling upon another with evil intent since such is within the global range of naphal. Though the word has an “uncertain etymology,” Gesenius, a great exegete, considered this a possibility as he states that the word may refer to “causing men to fall from fear.”
The word Nephilim most clearly means “giants” (BDB). These Nephilim were described as “mighty men who were of old, men of renown.” The same word is used after the flood by the Israelite spies who went into the Promised Land and saw Nephilim, “men of great size” (Num. 13:32-33). In that context they are described as men, apparently perceived to be hostile enough that ten spies lobbied against entering a land with men of such stature that the spies seemed “like grasshoppers” in their own eyes and to the Nephilim. Goliath comes to mind.
Finally, Ezekiel 32:21 uses the descriptive word for the Nephalim found in these earlier passages, gibbor, translated in English as “mighty ones.” The Septuagint (the Greek translation of the OT) translates with the word “gigantes,” again referring to men of great stature and from which we get our word “giant.” Ezekiel is not talking about angels, but about men whose height and size was unusually large.
So, I interpret that “Nephilim” are warriors of great physical stature, able to “fall” upon their enemies with great success and thereby gain great notoriety.
To assume, as some have argued, that evil angels can come to earth, assume the form of man, and produce children is an extremely unbiblical and upsetting idea. It leaves the earth open to great demonology. Nowhere is this threat addressed in Scripture. If such reproduction can and does indeed happen, the silence of the Bible on such a destructive force is inconceivable. To develop this idea from one murky verse is irresponsible-especially when there are other viable understandings.
While care should be used about being “dogmatic” on the interpretation of Gen. 6:1-4, I am very satisfied with the above interpretation as faithful to the text and to the entirety of Scripture.