The word interstices 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 interstices
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Seven Letter Word Alert: (54 words)
censers, centers, centres, cerises, cistern, citrine, cittern, cresset, cretins, enteric, enticer, entices, entries, iciness, incests, incises, inciter, incites, insects, inserts, irenics, nesters, netters, nitrite, nittier, recites, renests, resects, resents, retests, retints, scenter, screens, secerns, secrets, seitens, sericin, sestine, setters, sincere, sinters, sitters, streets, tensest, tenters, tentier, tersest, testers, testier, tiniest, tinters, tintier, trienes, trisect