The word onomasticons 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: 20
Highest Scoring Words With Friends™ Plays In The Letters onomasticons
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Seven Letter Word Alert: (31 words)
actions, amnions, anoints, atomics, atonics, caisson, cantons, casinos, cassoon, cations, consist, contain, incants, mansion, mascots, masonic, miscast, monocot, monsoon, mosaics, motions, nations, notions, oncosis, osmotic, scotoma, sitcoms, somatic, somonis, stannic, tocsins