Cakra-saṃvara (Sanskrit; Tib., bde-mchog 'khor-lo). Literally ‘The Wheel of Supreme Bliss’, a semi-wrathful yi-dam or tutelary deity with four heads and twelve arms associated with a particular group of anuttara-yoga Mother Tantras. He is also known by the short form of his name, Saṃvara or alternatively Śaṃvara. Normally he is depicted in union with his consort Vajra-Varāhi. See also Cakra-saṃvara Tantra.

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