bluff (n.1)

"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.

bluff (n.2)

an alternative name for the game of poker, 1824; see bluff (v.). As "an act of bluffing" by 1864. To call (one's) bluff is from 1876.

bluff (v.)

1839, "to deceive (opponents), especially by betting heavily and with a confident air on a worthless hand to make them 'fold,'" an American English poker term, perhaps from Dutch bluffen "to brag, boast," or verbluffen "to baffle, mislead." The general sense "use a show of confident assurance to deceive an opponent as to one's real resources or strength" is by 1854. Related: Bluffed; bluffing.

An identical word meant "blindfold, hoodwink" in 1670s, but the sense evolution and connection are unclear; OED calls it "one of the numerous cant terms ... which arose between the Restoration and the reign of Queen Anne."