The term 'Cinnamon Source' can be broken down into two crossword solutions: 'BARK' (4 letters) and 'CASSIA' (6 letters). Cinnamon is a spice derived from the inner BARK of trees in the genus Cinnamomum. The most common source of cinnamon is the BARK of the Cinnamomum CASSIA tree, which is also known as 'CASSIA' or 'Chinese Cinnamon'. The BARK of this tree is harvested, dried, and ground into a powder to produce the familiar cinnamon spice.