The term SILK SOURCE is composed of four words: SOY (3 letters), ERI (3 letters), ERIA (4 letters), and COCOON (6 letters). SOY is a type of bean that is used to make a variety of products, including silk. Eri is a type of silkworm native to India and is the primary source of eri silk. Eria silk is a type of silk made from the cocoons of eri silkworms. COCOON is the protective casing spun by the silkworm larvae, which is then harvested to make silk. Together, these four words form the term SILK SOURCE, which refers to the origin of silk.