The word unimaginably 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: 26
Highest Scoring Words With Friends™ Play In The Letters unimaginably
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Seven Letter Word Alert: (20 words)
albumin, alumina, ambling, amiably, anginal, bailing, blaming, bulimia, lambing, limning, mailbag, mailing, mangily, mauling, myalgia, nailing, numbing, unalign, unbalmy, unmanly