The Jesuits built a Chapel on the hill (near the present day railway station) and named it after Mount Zion in Jerusalem. The Marathi name is a corruption of the word Shiva, which means boundary or limit?

Sion in Mumbai gets its name from the Portuguese 'Sião' (after Mount Zion in Jerusalem), and the Jesuits did build a chapel there. The Marathi word 'Shiva' (शीव) means boundary or limit, which is what Sion historically marked - the boundary between Bombay and Salsette Island. Bandra, Elphinstone Road, and Byculla don't fit this historical description.