鈷 character

Language and compound decide.

Chinese chemistry uses 鈷 for cobalt. Japanese Buddhist compounds use it in vajra names: a ritual implement adapted from an Indian weapon, used in esoteric Buddhism to overcome delusion.

Older dictionaries list 鈷 as a smoothing iron or ritual vessel. A bronze example dates to the Warring States. Japanese 独鈷 appears in the Wamyōshō, an early Japanese dictionary, circa 934; cobalt is a 19th-century scientific borrowing.