Vajra-śekhara Tantra 

1. The ‘Diamond Pinnacle Tantra’, a supplementary text, surviving only in Tibetan translation, to the Sarva-tathāgata-tattva-saṃgraha. The supplementary text elucidates a series of questions arising from the root tantra.

2. The title generally given in its Chinese equivalent to those portions of the Sarva-tathāgata-tattva-saṃgraha which were translated into Chinese by Vajrabodhi, Śubhākarasiṃha, and Amoghavajra during the T'ang dynasty.

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