The word retrogressing 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: 18
Highest Scoring Words With Friends™ Play In The Letters retrogressing
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Seven Letter Word Alert: (97 words)
eggiest, egoists, engorge, engross, entries, erotise, estrone, genesis, gingers, girners, goiters, goitres, goriest, greisen, grister, grosser, ignores, inerter, ingests, ingress, inserts, integer, ironers, negroes, nestegg, nesters, norites, nosiest, orients, regents, regions, regorge, regress, regrets, reigner, reinter, renests, renters, rerents, rerinse, resents, resigns, resorts, resters, resting, restirs, restore, retirer, retires, retries, riggers, ringers, rinsers, rioters, roister, rosiest, rosters, seitens, seniors, serging, sestine, signees, signers, signets, signors, singers, sinters, snogger, snorers, snorter, soggier, soirees, sorrier, sorters, sorties, sorting, stenose, stereos, sterner, stinger, stirrer, stogies, stoners, stonier, stories, storing, strings, tensors, terrier, terroir, terrors, tigress, tossing, treeing, trienes, trigger, triones