The word luminescing 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: 23
Highest Scoring Words With Friends™ Play In The Letters luminescing
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Seven Letter Word Alert: (23 words)
ceiling, cuisine, emulsic, emulsin, ensuing, incline, inlines, insulin, inulins, legumin, lensing, leucism, lignins, limning, linings, menisci, mincing, mingles, slicing, sliming, smiling, uncling, unsling