The word slathered 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: 13
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (42 words)
adheres, alerted, altered, dealers, dearest, dearths, delates, earthed, elaters, halters, hardest, hatreds, headers, headset, healder, healers, hearsed, hearted, heaters, heralds, lathers, leaders, leadeth, leashed, leather, realest, reasted, redates, redeals, redealt, reheats, related, relates, sedater, sheared, shelter, slather, stealer, tasered, threads, trashed, treadle