The word interpenetration cannot be made in Words With Friends™. It is 16 letters long, too long to fit on a WordsWithFriends board (15 letters max).
Highest Scoring Words With Friends™ Plays In The Letters interpenetration
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Seven Letter Word Alert: (88 words)
airport, arenite, attirer, attrite, entente, enterer, entrain, entrant, entreat, etaerio, inepter, inerter, inertia, intoner, iterate, nattier, neonate, ninepin, nitrate, nitrene, nitrite, nittier, operant, operate, ornater, otarine, painter, partner, patient, patriot, pattern, peatier, pennant, pentane, pentene, pertain, pettier, pinnate, pioneer, pointer, pontine, portent, pottant, praetor, prairie, preener, prenote, preteen, printer, pronate, prorate, protean, protein, rainier, rattier, reenter, reinter, repaint, repiner, repoint, reprint, retiree, retrain, retreat, taperer, tattier, tearier, teenier, tentier, ternate, terpene, terpine, terrain, terrane, tinnier, tintier, tiptoer, titrate, tonette, torrent, trainee, trainer, traitor, treater, treetop, triaene, triptan, trotter