The word fishtailing 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 fishtailing
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Seven Letter Word Alert: (28 words)
aflight, aisling, alights, anglist, failing, fasting, filings, finials, fishing, flights, hailing, halting, initial, insight, intagli, lashing, lasting, lathing, lifting, listing, sailing, salting, sifting, silting, slating, tailfin, tailing, tilings