The two crossword solutions for the term 'Neighbor of Sumatra' are JAVA and Nias. JAVA is an Indonesian island located in the Indian Ocean, just east of Sumatra. It is the most populous island in Indonesia and the 13th largest island in the world. Nias is an Indonesian island located off the western coast of Sumatra. It is known for its unique culture and traditional architecture. Both JAVA and Nias are part of the Indonesian archipelago and are neighbors of Sumatra.