The word heartlessness 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: 17
Highest Scoring Words With Friends™ Play In The Letters heartlessness
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Seven Letter Word Alert: (81 words)
anthers, antlers, arsheen, artless, ashless, assents, asserts, earless, earnest, earthen, eastern, elaters, enseals, ensears, enteral, enthral, entrees, eternal, ethanes, ethenes, halters, harness, hassles, hastens, hatless, healers, hearses, hearten, heaters, lashers, lateens, lathers, leaners, leanest, leasers, leashes, leather, lessees, lessens, nearest, nesters, nestles, netless, rashest, realest, reheats, reheels, relates, release, relents, renests, rentals, resales, reseals, reseats, resents, reslant, saltern, sateens, sealers, seaters, seether, seethes, senates, sensate, sheeter, shelter, slasher, slashes, slaters, slather, stashes, stealer, sterane, sternal, tassels, tealess, teasels, teasers, trashes, tresses