Originally, the word 'tantra' seems to have meant any science or body of knowledge. Gradually, however, it got restricted to a particular class of literature, a literature primarily devoted to the cult of Saktiand containing an amalgam of religion, philosophy, esoteric and occult rites, astronomy, astrology, medicine and prognostications. In this respect, the tantras resemble the puranas. Etymologically the word is derived from its two constituents 'tan,' to spread; 'trai,' to protect and is supposed to mean any work that spreads or dilates upon many matters like tattvas (fundamental principles) and mantras (sacred words and syllables) and through that knowledge affords protection to the votaries.