Yes, bet is a Scrabble word!
...and is worth 5 points in Scrabble, and 6 points in Words with Friends
bet
Verb
1. Maintain with or as if with a bet
2. Stake on the outcome of an issue
3. Have faith or confidence in
Noun
1. The money risked on a gamble
2. The act of gambling
What Scrabble words can I make with the letters in bet?
2 Letter Words