The word backcrossing 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: 28
Highest Scoring Words With Friends™ Play In The Letters backcrossing
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Seven Letter Word Alert: (41 words)
agnosic, arkosic, backing, barking, basking, bonsais, boracic, borings, bossing, bracing, braking, brogans, broking, caisson, carbons, carsick, casings, casinos, cassock, coaking, cocking, cognacs, corking, cosigns, isobars, organic, racking, rocking, sabinos, sacking, scaring, scoriac, scorias, scoring, sickbag, signora, signors, soaking, soaring, socking, sringas