Cadmium (element)
鎘 is a character created specifically to name the chemical element cadmium. It has no broader conceptual center beyond this technical use.
鎘 is a modern coined character for cadmium, combining the metal radical 金 with the phonetic component 鬲 (reki/kaku). It was created in the 19th–20th century for chemical nomenclature and has no ancient origin.
The metal radical 金 tells you this is a metallic element. The right side 鬲 looks like a complex container—imagine a special metal vessel holding cadmium.
For レキ, picture a chemist saying 'Let's add a speck of cadmium'—'recky' sounds like レキ and ties to the metal's use in small amounts.