also blue-grass, music style, 1958, in reference to the Blue Grass Boys, country music band 1940s-'50s, from the "blue" grass (Poa pratensis) characteristic of Kentucky, the grass so called from 1751. Kentucky has been called the Bluegrass State since at least 1872; see blue (n.) + grass.[bluegrass etymology, bluegrass origin, 英语词源]