bluff (v.) Look up bluff at Dictionary.com
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."
bluff (n.1) Look up bluff at Dictionary.com
"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) Look up bluff at Dictionary.com
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.