The first occurrence.
And he shall besiege you in all your gates, until your high and fenced walls come down, in which you trusted, throughout all your land: and he shall besiege you in all your gates throughout all your land, which the LORD your God has given you. Deu 28:52
The primitive root.
Strong’s H982 בטח batach, a primitive root meaning, “to trust.” The 3-letter root is bet + tet + chet.
bet ב = the house, thus house, household, family, in, within
tet ט = the basket, thus surround, contain, hold, mud
chet ח = the wall, thus outside, divide, half
The story: The family (bet) surrounded by (tet) the wall (chet). The abstract concept from this verbal root is security, because the family is secure within its house.