1758, originally Scottish, "seat, bench," of uncertain origin, possibly a variant of banker "bench" (1670s; see bank (n.2)); possibly from a Scandinavian source (compare Old Swedish bunke "boards used to protect the cargo of a ship"). Of golf courses, first recorded 1824, from extended sense "earthen seat" (1805); meaning "dug-out fortification" probably is from World War I.
