The word spontaneousness 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: 22
Highest Scoring Words With Friends™ Play In The Letters spontaneousness
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Seven Letter Word Alert: (48 words)
aptness, asepses, assents, espouse, eupneas, eupnoea, neatens, neonate, nonanes, nonenes, nonsane, nonstop, noseans, oneness, onestep, openest, osseous, osteons, outsees, outspan, passout, peanuts, pennant, pentane, pentose, poetess, possess, possets, poteens, sateens, seasons, senates, sensate, sonnets, soonest, spouses, stenose, stepson, sunsets, sunspot, suntans, tossups, toupees, uneaten, unseats, unsnaps, unspent, unstops