The word whistlestop 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 whistlestop
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Seven Letter Word Alert: (30 words)
holiest, hoplite, hostels, hostile, isohels, owliest, pettish, pistols, pitless, postils, potties, pottles, shitpot, slowest, slowish, spittle, spotlit, stewpot, theists, thistle, tipless, tiptoes, toilets, topless, twostep, whistle, whitest, whittle, wholist, witless