The Soka Gakkai Dictionary of Buddhism
namu[南無] ( Jpn; Skt namas )
Also pronounced nam. A transliteration of the Sanskrit word namas, meaning devotion. The word namu expresses a feeling of reverence and devotion and is placed before the names of objects of veneration such as Buddhas, bodhisattvas, deities, sutras, the truth, and the three treasures of Buddhism (the Buddha, his teachings, and the Buddhist Order). "Namu Amida Butsu," the phrase invoked in the Pure Land school in general, means "Homage to Amida Buddha" or "I take refuge in Amida Buddha." "Nam-myoho-renge-kyo" is the invocation in Nichiren's teachings, meaning devotion to Myoho-renge-kyo, or the title and essence of the Lotus Sutra.