The word arithmetical 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: 21
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (48 words)
achiral, airmail, airtime, alethic, archeal, archlet, article, attache, caramel, cattail, cattier, chattel, chatter, chimera, ciliate, citrate, claimer, clatter, climate, clitter, ethical, imitate, itchier, lactate, lattice, limiter, mailcar, maltier, marital, marlite, martial, matcher, metical, militar, miracle, ratchet, rattail, recital, reclaim, rematch, tactile, teacart, tertial, thalami, thermal, thermic, titmice, trachea