付

Left indexing person radical 亻 — left-side form of 人. Anchors 付 in the human-interaction family alongside 信 (trust), 任 (responsibility), 仰 (look up to), 借 (lend). Paying is fundamentally a transaction between persons.

Right 寸 — pictograph of a hand with a small dot marking the wrist-pulse, the ancient anatomical reference for the "inch." Here 寸 functions as a hand: 付 depicts one person handing something over to another with measured care. A textbook 会意字 (compound ideograph) — handing-over-by-hand, the original picture of payment.