Or “Great Spike of Purity,” the name of a bodhisattva. Possibly śaṅku is a misreading or misspelling of sanatku, which would be “the bodhisattva Sanatkumāra” (Pali: Sanaṅkumāra), who was a being of the class of Mahābrahmās‍—in Vedic legend, one of the four or seven “mind-born” sons of Brahmā‍—and who appears in various suttas in the Pali canon.