Genesis 6:4

The Nephilim i.e. giants. It is natural to refer to Numbers 13:33, "And there we saw the Nephilim (Or, giants), the sons of Anak, which come of the Nephilim; and we were in our own sight as grasshoppers, and so we were in their sight." The tradition that the Nephilim existed at the time of the Exodus was therefore quite strongly held. The precise meaning of the name has been lost. The passage in Numbers shews clearly that it denoted men of gigantic stature. The etymology very probably goes back to primitive times; and its origin is lost with the dialects that disappeared when the Israelites finally occupied Palestine. It was natural to connect the word with the Hebrew naphal, "to fall"; hence arose the renderings of Aquila, οἱ ἐπιπίπτοντες, "the assailants," and of Symmachus, οἱ βιαῖοι, "the violent," while among Patristic commentators the word was connected with "the fallen angels." But these are merely guesses; and we must be content to leave the etymology of "the Nephilim," like that of "the Rephaim" and "the Anakim," unexplained.

and also after that These words are introduced very awkwardly; and were very probably added as a gloss, in order to shew that the Nephilim existed not only in primitive ages, but also at the time of the Exodus from Egypt, as would be implied by Numbers 13:33. The continuance of the Nephilim in later times seems to contradict the account of the destruction of all the dwellers on the earth by the Flood. This contradiction is to be explained on the supposition, mentioned above, that the present passage is a fragment of a tradition in which the Flood was not recorded.

the mighty men, &c. That is to say, "the well-known giants of old-world time," familiar personages in Israelite folk-lore. To this class belong such names as "Nimrod," Genesis 10:8, and "Og," Deuteronomy 3:11.

the men of renown Literally, "the men of name," as in Numbers 16:2, "men of renown," Lat. viri famosi, viz. famous for deeds of prowess and audacity.