1) An indestructible substance which is sometimes equated with emptiness; sometimes used as an adjective to indicate the quality of the substance.

2) A Dharma-implement.
 

"Vajra is a Sanskrit word which defies translation because of its numerous connotations, but essentially vajra is an indestructible substance, usually represented by diamond." (VS 3)

"Vajra has three meanings: durable; luminous; and able to cut. Vajra is so durable it cannot be destroyed by anything, but can itself destroy everything.

"'If vajra breaks up everything, then I won't have anything, and of what use will that be?' you may ask.

"The reason you don't realize Buddhahood is just because you 'have everything'. If you didn't have anything, you could realize Buddhahood. 'Everything' refers to your attachments--all those things you cannot put down. . . .

"Durable vajra breaks through thought, but not through no thought. The vajra of no thought is durable enough to smash all existing marks--all conditioned marks subject to outflows. No thought can destroy the spiritual penetrations of heavenly demons and those of external ways, because their spiritual penetrations have marks. . . .

"Vajra is luminous. Its light can break up all darkness. Vajra is able to cut. A sharp knife can sever something with a single slice, while a dull knife saws and saws and still cannot cut through. Vajra severs all the deviant knowledge and views of heavenly demons and those of external ways, chops through people's afflictions, and slices through ignorance." (VS 81)

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1) Chinese Mandarin: jin gang ; 2) Sanskrit: vajra.

See also: Vajra Prajna Paramita Sutra.

Buddhist Text Translation Society (http://www.BTTSonline.org) References: VS 3, 81.