The word gravestone 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
Seven Letter Word Alert: (44 words)
argents, atoners, avenger, avenges, earnest, eastern, engrave, enrages, estrone, garnets, gearset, goatees, governs, grantee, gravest, greaten, grovets, nearest, negates, negroes, onstage, oranges, overage, overate, overeat, oversat, oversea, overset, reagent, regents, restage, revotes, roseate, seagoer, senator, servant, sterane, storage, strange, taverns, treason, veteran, vetoers, voteens