The word shoestring 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: 15
Highest Scoring Words With Friends™ Plays In The Letters shoestring
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Seven Letter Word Alert: (57 words)
egoists, engross, goiters, goitres, goriest, heroins, histone, hogties, hornets, horsing, hosiers, hosting, hotness, ignores, ingests, ingress, inserts, inshore, norites, nosiest, ogreish, orients, regions, resight, resigns, resting, rosiest, seniors, shiners, shoeing, shoring, shorten, shrines, sighers, sighter, signers, signets, signors, singers, sinters, sorties, sorting, stinger, stogies, stoners, stonier, stonish, stories, storing, strings, tensors, thiones, thrones, throngs, tigress, tossing, triones