The word unrelentingly 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: 23
Highest Scoring Words With Friends™ Play In The Letters unrelentingly
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Seven Letter Word Alert: (31 words)
eluting, gentile, gentler, genuine, greenly, gruntle, gunnery, inertly, integer, leering, lenient, liturgy, nitrene, nullity, nunnery, reeling, relying, renting, retying, reunite, ringlet, running, telling, tingler, treeing, trunnel, turning, untying, uterine, yelling, yenning