Yes, mull is a Scrabble word!
...and is worth 6 points in Scrabble, and 10 points in Words with Friends
mull
Verb
1. Reflect deeply on a subject
2. Heat with sugar and spices to make a hot drink
Noun
1. A term used in Scottish names of promontories
2. An island in western Scotland in the Inner Hebrides
What Scrabble words can I make with the letters in mull?
3 Letter Words
2 Letter Words