The word diagonalisation 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™ Play In The Letters
Seven Letter Word Alert: (75 words)
against, agatoid, agnosia, agonist, aisling, analogs, anginal, anginas, angioid, anglist, anodont, anoints, antlion, atonias, atoning, daltons, datalog, dialing, dialogs, digital, dinting, galoots, goannas, gonadal, gondola, idolist, indians, indigos, initial, inlands, intagli, isodont, ladings, lagoons, landing, lasagna, lasting, liaison, ligands, lignins, linings, listing, loading, loaning, loosing, looting, lotions, nailing, nanodot, nations, noloads, nongoal, nongods, nongold, noosing, notions, oligist, onloads, sailing, salting, sanding, sidling, silting, slating, sliding, soiling, soloing, sooting, stoning, tailing, talonid, tidings, tilings, toiling, tooling