The word grindstones 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: 16
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (91 words)
denting, dentins, designs, digests, digress, dinners, dissent, dogsits, dossier, droning, editors, egoists, endings, engross, ensigns, eroding, godsent, goiters, goitres, goriest, grinned, groined, grossed, ignored, ignores, indents, indorse, ingests, ingress, inserts, intends, interns, intoned, intoner, intones, introns, negroid, nesting, nondiet, norites, nosiest, orients, redoing, regions, rending, renting, resigns, resting, rodents, roisted, rosiest, rosined, sending, seniors, sensing, signers, signets, signors, singers, sinners, sinters, snidest, snoring, snorted, sodgers, sonnets, sortied, sorties, sorting, steroid, stinger, stogies, stoners, stonier, stoning, storied, stories, storing, strides, strings, tending, tendons, tensing, tension, tensors, tierods, tigress, tinders, tinners, tossing, triones