Vajra, in Sanskrit, has both the meanings of “thunderbolt” and “diamond.” Like the thunderbolt, the vajra cleaves through ignorance. The thunderbolt was originally the symbol of the Hindu rain god Indra (who became the Buddhist Śakra) and was employed by the 8th-century Tantric (esoteric) master Padmasambhava to conquer the non-Buddhist deities of Tibet. Like the diamond, the vajra destroys but is itself indestructible and is thus likened to śūnya (the all-inclusive void).

The vajra is fashioned out of brass or bronze, the four prongs at each end curving around the central fifth to form a lotus-bud shape. A nine-pronged vajra is less commonly used.

In ritual use the vajra is frequently employed in conjunction with the bell (Sanskrit ghaṇṭā; Tibetan dril bu), the various gestures (mudrās), when correctly executed, having considerable metaphysical power. The vajra (symbolizing the male principle, fitness of action) is held in the right hand and the bell (symbolizing the female principle, intelligence) in the left hand, the interaction of the two ultimately leading to enlightenment. In art the vajra is an attribute of many divinities, such as the celestial Buddha Akṣobhya and his manifestation as a bodhisattva (“Buddha-to-be”), Vajrapāṇi (In Whose Hand Is the Vajra). The viśva-vajra is a double vajra in the shape of a cross with four equal arms.