round-shaped storage bin for grain
囷 centers on a round container for storing grain, specifically a round-shaped storage bin.
囷 combines 囗 (enclosure) with 禾 (grain), suggesting a container for grain. The round shape is implied by the enclosure.
The outer 囗 is an enclosure, and inside is 禾 (grain). Picture a round bin filled with grain.
For キン, imagine a king's round grain bin: king -> キン, and the bin is full of grain.