grain, corn
糓 centers on grain and corn as staple crops, referring to the harvested seeds used for food.
The exact historical development of 糓 is uncertain. It visually contains 米 (rice/grain) inside a complex outer structure that may have contributed sound or meaning, but the original component relationships are not clear.
Picture 米 (rice) tucked safely inside a sturdy granary (the surrounding structure). The grain is stored and protected, representing grain and corn.
For コク, imagine a cook inspecting the stored grain: cook -> コク, and the cook checks the 米 inside the granary.