The word diagonalise 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: 16
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (56 words)
adonise, aeolian, agendas, agnosia, agonies, agonise, aisling, aliased, aligned, analogs, angioid, anilide, anodise, dailies, dangles, dealign, dealing, denials, dialing, dialogs, dingies, doilies, eliding, elision, eloigns, galenas, genials, geoidal, goalies, goldens, gonadal, idolise, indigos, indoles, iodines, ionised, ladings, lasagne, leading, leasing, legions, liaised, liaison, ligands, lingoes, lionise, loading, sailing, sealing, sealion, sidling, singled, slanged, sliding, snailed, soiling