The word dissimilarity is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 20
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (24 words)
aridity, diarist, dirtily, disarms, dismals, dismays, distils, lyrists, midairs, militar, militia, misdial, mislaid, mislays, missaid, mistily, mistral, myriads, similar, smartly, tardily, timidly, trysail, tsarism