What is the meaning of Vajra?

A Buddhist ceremonial mace and symbol, usually interpreted as both a diamond and a thunderbolt.

One of the five central Buddhist principles, representing indestructible substance that cuts and penetrates through emotional instability or uncertainty.

The weapon of Indra, the god of heaven and the chief deity of the Rigvedic pantheon, used to kill sinners and ignorant persons.

sublative singular of vaj

Source: wiktionary.org