イン, いな, かず
employee, member, number, the one in charge
JLPT4 G3 S10 F54
The relevant oracle bone form of this character combines 囗# circular enclosure + a tripod kettle → (the *circumference* of a) *round*, tripod kettle → *number* (← counter for round objects ← round objects) → *member* (← number of people; compare the expression "per capita," along with the character 頁).
[Full Kanji Etymology List]