The Chinese translation is 真言; zhenyan; 'accurate text', the Japanese on'yomi looking through from the Chinese remaining shingon (that's also used as the right name for that Shingon sect). Quite a few ancient mantras are located in the Saṃhitā portion of the Vedas. The Saṃstrikeās are quite possibly the https://www.youtube.com/watch?v=ebjMeUz17Ro