The first occurrence.
In the beginning God Elohiym created the heaven and the earth. Gen 1:1
The primitive root.
Strong’s H7225 re’shiyth, a concrete noun meaning, “beginning, firstfruits;” from Strong’s H7218 rosh, a concrete noun meaning, “head;” from an unused, unnamed primitive root meaning, “to shake.” The 3-letter root of the noun is resh + aleph + shin.
resh ר = the head of man, thus head, first, top, beginning, man
aleph א = the ox head, thus strength, power, leader
shin ש = two front teeth, thus sharp, press, eat, two, again
The story: The head (resh) has the power (aleph) to give his assent or denial (shin, i.e., a head nod of assent or shake of denial is a movement made again and again).