Yes, quack is a Scrabble word!
...and is worth 20 points in Scrabble, and 22 points in Words with Friends
quack
Verb
1. Utter quacking noises
2. Act as a medical quack or a charlatan
Adjective
1. Medically unqualified
Noun
1. An untrained person who pretends to be a physician and who dispenses medical advice
2. The harsh sound of a duck
What Scrabble words can I make with the letters in quack?
3 Letter Words
2 Letter Words