The first occurrence.
And your life shall hang in doubt before you; and you shall fear day and night, and shall have no assurance of your life. Deu 28:66
The primitive root.
Strong’s H6342 פחד pachad, a primitive root meaning, “to fear, to be in dread.”
pey פ ף = the mouth, thus open, blow, scatter, edge
chet ח = the wall, thus outside, divide, half
dalet ד = the door, thus enter, move, hang
The story: One cognate word is “thigh;” as that which is normally steady, upholding the body. But when an opening (pey) has been made in the wall (chet, as that which upholds as the thigh upholds) the thigh moves to and fro (dalet, as a door on its hinges), that is, shakes with fear.
This is not the same word as is used in the phrase, “to fear YHVH,” found hundreds of times in the Hebrew Bible. That word is Strong’s H3372 ירא yare; “to fear what a man worships above himself as the greater.”