The word masterless 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: 14
Highest Scoring Words With Friends™ Play In The Letters masterless
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Seven Letter Word Alert: (35 words)
armless, armlets, artless, asserts, earless, elaters, leasers, masters, measles, melters, realest, relates, remates, remelts, resales, reseals, reseats, resmelt, restems, reteams, sealers, seamers, seaters, sesames, slaters, smelter, stealer, steamer, streams, tassels, tealess, teasels, teasers, tramels, tresses