steps, grade, strata, series
貤 centers on layered progression: steps in a sequence, grades or levels, strata, or a series of things arranged in order.
貤 combines 貝 (shell, money) with 也, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with the idea of transferring or layering value in steps.
Shells (貝) stacked beside a marker (也) suggest layers of value: steps, grades, or strata built up one after another.
For イ, imagine an easel (イーゼル) holding layered strata of shells: easel -> イ, and the shells form a series of steps.