The word plesiosaurs 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 plesiosaurs
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Seven Letter Word Alert: (51 words)
airless, arouses, asepsis, aspires, assures, issuers, lassies, lassoer, lassoes, leprous, lessors, lipases, lispers, lossier, lousier, oarless, palsies, paresis, paroles, passers, perusal, plusses, poseurs, praises, pulsars, pulsers, pussier, pussies, resails, resoils, sailers, sailors, sapless, sassier, serials, serious, slopers, soapers, soapier, soupier, spirals, spireas, spoiler, sporule, spousal, spouses, surpass, suspire, upraise, uprisal, uprises