wine glass
榼 centers on a container for drinking wine: a wine glass or cup, often with a lid or cover.
榼 combines 木 (wood) with 盍, which likely contributes the sound and the idea of a covered container. The character originally referred to a wooden wine vessel with a lid.
The left side 木 suggests a wooden object, and the right side 盍 looks like a covered dish. Picture a wooden wine glass with a lid: 榼.
For コウ, imagine a wooden wine glass being passed around at a cozy gathering: cozy -> コウ, and the wooden cup holds the wine.