Yes, pi is a Scrabble word!
...and is worth 4 points in Scrabble, and 5 points in Words with Friends
pi
Noun
1. The ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846...
2. Someone who can be employed as a detective to collect information
3. The scientist in charge of an experiment or research project
4. The 16th letter of the Greek alphabet
5. An antiviral drug used against HIV; interrupts HIV replication by binding and blocking HIV protease; often used in combination with other drugs