Why is the ninth month called September?
late 14c., "overgrown with trees and shrubs," from wood (n.) + -y (2). Of plants, "having a stem of wood," from 1570s. As a name for a kind of station wagon with wood panels, by 1961, U.S. surfer slang (real wood exterior panels were rare after 1951 and the last use of real wood was in the 1953 Buick Roadmaster Estate Wagon). Slang meaning "erection" attested by 1990 (for hardness).
The thick xylem of trees and shrubs, resulting from secondary growth by the vascular cambium, which produces new layers of living xylem. The accumulated living xylem is the sapwood. The older, dead xylem in the interior of the tree forms the heartwood. Often each cycle of growth of new wood is evident as a growth ring. The main components of wood are cellulose and lignin.