The word differentiable 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: 26
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (132 words)
affined, airlift, airline, alerted, altered, anilide, arenite, baffled, baffler, bailiff, bandlet, bartend, beadier, bedrail, beefier, beeline, beetled, belated, bendier, bendlet, benefit, berated, blander, bleated, bleater, bleeder, blender, blinder, brailed, brained, briefed, brindle, daffier, debater, debrief, deerlet, defiant, defiler, definer, deflate, deifier, deleter, deliria, denarii, detrain, dietine, dilater, draftee, driblet, edifier, eleidin, enabled, enabler, enteral, entered, eternal, fainted, fainter, fanbelt, febrile, federal, feebler, feedbin, fertile, fibered, fibrate, fielder, fifteen, filbert, fileted, filiate, fireant, firebed, firelit, flatbed, fleeted, fleeter, flirted, freebie, friable, inbreed, inditer, indraft, inertia, infidel, infield, inflate, latrine, leafier, learned, lenited, libated, lineate, lintier, needier, needler, niftier, nitride, raffled, ratline, rebaled, rebated, rebited, rebleed, reblend, reblent, redealt, redline, refiled, refined, reflate, reified, related, reliant, relined, retiled, retinal, riffled, tailfin, teenier, tenable, tendril, tradein, trailed, trained, trainee, treadle, trebled, trenail, triable, triaene, trifled