The Soka Gakkai Dictionary of Buddhism
sadhu[善哉] (Skt, Pali; Jpn zenzai or yokikana )
"Excellent," "Very good," or "Well done." An expression of praise and approval. A Buddha or a Buddhist teacher might use this word when praising or expressing approval, usually toward a disciple. In Buddhist scriptures, this word is often repeated for emphasis, appearing in English translations as "Excellent, excellent!" or "Well done, well done!" In the "Treasure Tower" (eleventh) chapter of the Lotus Sutra, the Buddha Many Treasures speaks from within the jeweled tower, saying: "Excellent (sadhu), excellent (sadhu)! Shakyamuni, World-Honored One, that you can take the great wisdom of equality, a Law to instruct the bodhisattvas, guarded and kept in mind by the Buddhas, the Lotus Sutra of the Wonderful Law, and preach it for the sake of the great assembly! It is as you say, as you say. Shakyamuni, World-Honored One, all that you have expounded is the truth!" Sadhu also means upright, good, honorable, righteous, or correct, and also indicates a holy man or a sage.