The word antagonises 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: 15
Highest Scoring Words With Friends™ Play In The Letters antagonises
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Seven Letter Word Alert: (39 words)
against, agatine, agatise, agnosia, agonies, agonise, agonist, anginas, anoints, antigen, atonias, atoning, egoists, ensigns, gentian, goannas, ingests, intones, nations, nesting, noseans, nosiest, onstage, sagiest, seating, seitans, sensing, sestina, siennas, signets, sonatas, sonnets, stogies, stoning, teasing, tensing, tension, tonnage, tossing