The word diagnostics 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: 18
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (30 words)
actions, agnosic, agonist, angioid, atonics, caisson, casings, casinos, casting, cations, coating, codings, conidia, consist, cosigns, costing, diction, discant, dissing, dogsits, gnostic, iconist, indicts, indigos, nicosia, sidings, sinoids, tidings, tocsins, tossing