ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ noun
Etymology: yellow (I) + back
1. : gold certificate
2. : a cheap and usually sensational novel ; especially : one sold in yellow board or paper covers in the late 19th and early 20th centuries
3. : a freshwater mussel ( Lampsilis anodontoides ) of the Mississippi valley and southeastern United States having a heavy shell covered with yellow periostracum and highly valued for mother-of-pearl