white millet
芑 refers specifically to white millet, a type of grain. The meaning is narrow and concrete.
芑 combines the grass radical 艹 with 己, which likely acts as a phonetic component. The character is used for a specific plant, white millet.
The grass radical 艹 sits above 己, like a plant with a distinctive shape. Picture a field of white millet growing under the sun.
For キ, imagine a key made of white millet stalks: key -> キ, and the key unlocks the grain's name.