Yes, cook is a Scrabble word!
...and is worth 10 points in Scrabble, and 11 points in Words with Friends
cook
Verb
1. Prepare a hot meal
2. Prepare for eating by applying heat
3. Transform and make suitable for consumption by heating
4. Tamper, with the purpose of deception
5. Transform by heating
Noun
1. Someone who cooks food
2. English navigator who claimed the east coast of Australia for Britain and discovered several Pacific islands (1728-1779)
What Scrabble words can I make with the letters in cook?
3 Letter Words