bunker

The earliest sense of bunker was a box or chest whose lid doubled as a seat, from Scots bunker (a bench, pew, or window-seat, also a coal receptacle or sand pit in golf). This traces to Early Scots bunker/bunkur, probably from Old Norse bunki ("a heap"), itself from Proto-Germanic *bunkô ("a heap, pile, bump"), possibly rooted in Proto-Indo-European words for "thick" or "to swell."

From a humble seat-chest and coal bin, the word passed into German as Bunker ("large bin or container for storing coal") and was borrowed back into English during World War II to mean a hardened shelter against bombs and attack.

Bunk, the sleeping berth on a ship or train, likely comes from the same Old Norse root bunki, meaning both words descend from an old idea of a stacked or heaped-up thing.