jewel
珂 centers on a jewel or precious stone, often used in ornamental contexts.
珂 combines 王 (jewel) with 可, which likely contributes the sound. The character is used for ornamental stones or jewels.
The left side 王 (jewel) and right side 可 (possible) suggest a jewel that is possible to obtain or admire. Picture a beautiful jewel that you can hold.
For カ, imagine a jewel that is so bright it makes you say 'car!' because it shines like a car's headlight: car -> カ.