"broad, vertical cliff," 1680s, from bluff (adj.) "with a broad, flat front" (1620s), a sailors' word, probably from Dutch blaf "flat, broad." Apparently a North Sea nautical term for ships with broad bows and flat vertical stems. It was later extended to landscape features in North America, such as high broad banks along a shore or range of hills. Of persons, in reference to a full face, indicative of frankness and rough good humor, 1808.