vajra

(Sanskrit; Tib., rdo-rje). Originally, the thunderbolt weapon of the vedic god Indra in early Indian religion, the term later also denoted a diamond. The Buddhist use of the term combines these two meanings to connote the indivisible and imperishable nature of enlightenment (bodhi). While maintaining this significance in its literature, a vajra in tantric Buddhism also refers to the double-headed ritual implement, usually made of metal, with one, three, five, or nine prongs at each end. When paired with the ritual bell (ghaṇṭā) in Tibetan Buddhism, the vajra symbolizes skilful means (upāya-kauśalya) in contrast to insight (prajñā). In Japanese Shingon, the vajra is associated with the concept of the Vajra Realm which is derived from the Sarva-tathāgata-tattva-saṃgraha.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)

vájra m. n. 'the hard or mighty one', a thunderbolt (esp. that of Indra, said to have been formed out of the bones of the Ṛishi Dadhīca or Dadhīci q.v., and shaped like a circular discus, or in later times regarded as having the form of two transverse bolts crossing each other thus x

• sometimes also applied to similar weapons used by various gods or superhuman beings, or to any mythical weapon destructive of spells or charms, also to manyu, 'wrath' RV. or [with apām] to a jet of water AV. &c. &c

• also applied to a thunderbolt in general or to the lightning evolved from the centrifugal energy of the circular thṭthunderbolt of Indra when launched at a foe

• in Northern Buddhist countries it is shaped like a dumb-bell and called Dorje

• See MWB. 201 ; 322 &c.) RV. &c. &c

• a diamond (thought to be as hard as the thunderbolt or of the same substance with it), ṢadvBr. Mn. MBh. &c

• a kind of talc L

• a kind of penance (feeding for a month on only barley prepared with cow's urine) L

• sour gruel W

• m. a form of military array, Mī. MBh. &c. (cf. -vyūha)

• a kind of column or pillar VarBṛS

• a partic. form of the moon ib

• a partic. Ekāha, Vtit

• a kind of hard mortar or cement (kalka) VarBṛS. (cf. -lepa)

• N. of the 15th of the 27 Yogas or astronomical divisions of time ib

• a partic. Soma ceremony ṢaḍvBr

• Euphorbia Antiquorum and another species L

• Astera L

• N. of a mountain R

• of an Asura Virac

• of a son of Aniruddha MBh. Hariv. Pur

• of a son of Vilvamitra MBh

• of a son of Manu Slvarṇa Hariv

• (with Jainas) of one of the 10 Dala-pūrvins L

• of a Ṛishi VarBṛS. (v. l. for vātsya)

• of a minister of Narendrāditya Rājat

• of a son of Bhūti ib

• of a heretical king Buddh

• (ā), f. Cocculus Cordifolius L

• Euphorbia Antiquorum or Tirucalli L. N. of Durgā, DeviP

• of a daughter of Vaisvanara VP

• (ī), f. a kind of Euphorbia L

• n. denunciation in strong language (compared to thunder) R. Sāh. Pratāp. (cf. vākya- and vāg-v○)

• a kind of hard iron or steel L

• a partic. posture in sitting Cat. (cf. vajrâsana)

• N. of a partic. configurations of the planets and stars (in which favourable planets are situated in the 1st and 7th houses and unfavourable in the 4th and 10th) VarBṛS

• myrobolan L

• the blossom of the sesamum or of any plant called Vajra L

• Andropogon Muricatus L

• = bālaka, a child, pupil L

• mfn. adamantine, hard, impenetrable W

• shaped like a kind of cross (cf. above), forked, zigzag ib. [Cf. Zd. vaśra, 'a club.'] [Page 913, Column 2]

Sanskrit-English Dictionary, by M. Monier William

rdo rje

[translation-san] {MSA,C} vajra

[translation-eng] {Hopkins} vajra; adamantine

[translation-eng] {C} diamond; thunderbolt

Jeffrey Hopkins' Tibetan-Sanskrit-English Dictionary