The word carthorses 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: 15
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (56 words)
actress, archers, arrests, carrots, carters, cashers, casters, castors, chaoses, charter, chasers, chaster, coarser, coaster, corsets, costars, crasher, crashes, crasser, craters, creator, crosser, earshot, escorts, hoarser, rashers, rashest, rasters, reactor, recasts, rechart, recoats, recross, rectors, reroast, resorts, rhetors, roaches, roaster, rosters, sachets, scarers, scathes, scorers, sectors, sharers, shorter, soarers, sorters, starers, torches, tracers, trasher, trashes, trocars, trochar