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."

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.

Definitions of bluff
bluff (n.)
a high steep bank (usually formed by river erosion);
bluff (n.)
pretense that your position is stronger than it really is;
his bluff succeeded in getting him accepted
bluff (n.)
the act of bluffing in poker; deception by a false show of confidence in the strength of your cards;
Synonyms: four flush
bluff (v.)
deceive an opponent by a bold bet on an inferior hand with the result that the opponent withdraws a winning hand;
Synonyms: bluff out
bluff (v.)
frighten someone by pretending to be stronger than one really is;
bluff (adj.)
very steep; having a prominent and almost vertical front;
a bluff headland
Synonyms: bold / sheer
bluff (adj.)
bluntly direct and outspoken but good-natured;
a bluff but pleasant manner
a bluff and rugged natural leader