The first occurrence.
There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown. Gen 6:4
The primitive root.
Strong’s H5303 nephilim; Gesenius says the meaning of this plural concrete noun is uncertain, but his preference is “those who fall upon, attack;” likewise Strong’s lists, “bully, tyrant, giant;” the noun is from Strong’s H5307 נפל naphal, a primitive root meaning, “to fall, to cause to fall, to fall upon.” The 3-letter root is nun + pey + lamed.
nun ן, נ = the seed, thus continue, heir, son
pey ף, פ = the mouth, thus open, blow, scatter, edge
lamed ל = the shepherd’s staff, thus teach, yoke, to, bind
The story: The son (nun) of the judge, i.e. the mouth (pey) speaking with authority (lamed), or the mouth which pronounces judgment.