salt pit, leisure, pot, drink
盬 centers on a container for salt or liquid: a salt pit, a pot, or something used for drinking. The leisure sense is likely an extension of the idea of resting by a salt pit or a drinking vessel, but the connection is loose.
盬 is a rare character whose exact historical development is uncertain. It visually combines 臣, 古, and 皿, but the original semantic and phonetic roles of these components are unclear.
The left side 臣 suggests a kneeling figure, while 古 and 皿 together evoke an old pot or dish. Picture someone kneeling by an ancient salt pit, using a pot to collect salt or drink.
For コ, imagine a small child (子, こ) playing by the salt pit with a tiny pot: 子 -> コ, and the child is enjoying leisure time.