large goblet, apt, fitting
卮 centers on a large drinking vessel, specifically a goblet. The sense of 'apt' or 'fitting' likely extends from the idea of a vessel being well-suited to its purpose or contents.
卮 is a pictograph of a drinking vessel, with the modern form retaining the shape of a goblet or cup. The exact historical development is uncertain, but the vessel origin is broadly accepted.
The shape of 卮 resembles a large goblet with a wide rim and a sturdy base. Imagine a fitting vessel perfectly designed to hold a generous drink.
For シ, picture a large goblet filled with a shimmering drink: the shimmering liquid cues シ, and the goblet is perfectly apt for the occasion.