The word melanoblast 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 melanoblast
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Seven Letter Word Alert: (36 words)
abalone, ablates, amoebas, ballast, ballets, ballots, baseman, batsman, batsmen, bellman, bemoans, benmost, bestman, boatman, boatmen, entombs, lambast, laments, leantos, losable, mallets, maltose, mantels, mantles, nabales, netball, noblest, notable, oatmeal, salable, sealant, stollen, tamable, tamales, tollman, tollmen