If you mean "to deceive by pretending to have something you don't":
* Feign: To pretend or give a false appearance of something.
* Fake: To imitate or counterfeit something.
* Deceive: To mislead or trick someone.
* Misrepresent: To present something falsely.
* Hoax: To deceive or trick someone by a fabricated story or situation.
If you mean "a steep cliff or slope":
* Cliff: A steep, high rock face.
* Precipice: A very steep cliff.
* Escarpment: A steep slope, especially one formed by faulting or erosion.
If you mean "a boastful or swaggering manner":
* Swagger: To walk or behave in a confident and arrogant way.
* Bravado: A bold, swaggering manner; false courage.
* Pretense: An attempt to create a false impression.
* Posturing: Behaving in a way that is intended to impress or intimidate others.
In the context of a poker game, "bluff" could be replaced with:
* Bet: To risk money on the outcome of a game or event.
* Raise: To increase the amount of money bet in a game of poker.
* Fold: To withdraw from a hand of poker.
Choose the synonym that best fits the specific meaning and context you're using "bluff" for.