late 14c., "overgrown with trees and shrubs," from wood, n. + -y(2). Of plants, "having a stem of wood," from 1570s. Related: Woodiness. Old English had wudulic. 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).