bunker (n.)

1758, originally Scottish, "seat, bench," a word of uncertain origin, possibly a variant of banker "bench" (1670s; see bank (n.2)); or possibly from a Scandinavian source (compare Old Swedish bunke "boards used to protect the cargo of a ship"). Meaning "receptacle for coal aboard a ship" is from 1839. Of sand-holes on golf courses, by 1824, from the extended sense "earthen seat" (1805). The meaning "dug-out fortification" probably is from World War I.