The word millimetres 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: 19
Highest Scoring Words With Friends™ Play In The Letters millimetres
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Seven Letter Word Alert: (34 words)
elitism, illites, immerse, itemise, limelit, limiter, melters, metrise, millers, millets, mistell, mistier, mistime, reemits, remelts, resmelt, retells, retiles, retills, retimes, rillets, sillier, siltier, slimier, slimmer, smeller, smelter, smilier, sterile, stiller, tellers, tellies, tillers, trellis