Yes, bluff is a Scrabble word!

Verb

1. Deceive an opponent by a bold bet on an inferior hand with the result that the opponent withdraws a winning hand

2. Frighten someone by pretending to be stronger than one really is

Adjective

1. Very steep; having a prominent and almost vertical front

2. Bluntly direct and outspoken but good-natured

Noun

1. A high steep bank (usually formed by river erosion)

2. Pretense that your position is stronger than it really is

3. The act of bluffing in poker; deception by a false show of confidence in the strength of your cards