The word mediastinum 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: 20
Highest Scoring Words With Friends™ Plays In The Letters mediastinum
:
Seven Letter Word Alert: (53 words)
amentum, ammines, animism, animist, aunties, dammits, destain, detains, diamine, dimmest, dummies, dunites, dustman, dustmen, indites, indiums, inmates, instead, maidens, medians, mediums, mindset, miniate, minimas, minimus, minuets, minutes, misdate, misedit, mismade, mismate, misname, mistime, mistune, munited, munites, sainted, sideman, sinuate, stadium, stained, stimied, summate, tandems, tediums, tsunami, unaimed, unities, unmated, unmates, unsated, untamed, untimed