The word diagonalising 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: (41 words)
agnosia, aisling, analogs, anginal, anginas, angioid, angling, dialing, dialogs, dinging, gaining, ganglia, gaoling, gilding, gliding, goading, goaling, goannas, gonadal, gosling, indians, indigos, inlands, ladings, landing, liaison, ligands, lignins, linings, loading, loaning, lodging, longing, nailing, sailing, sanding, sidling, signing, singing, sliding, soiling