The word mononuclear 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: 21
Highest Scoring Words With Friends™ Play In The Letters mononuclear
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Seven Letter Word Alert: (23 words)
almoner, cannolo, clamour, coalmen, corneal, coronal, enamour, leucoma, monocle, neuroma, nonamer, noncola, nonmale, nonmeal, nonreal, nuclear, nucleon, numeral, romance, unclean, unclear, unlearn, unmoral