“That’s not a word.” You can almost hear the know-it-all fifth grader saying it, hand on jutted hip, eye roll and all. You also might hear this from your editor. If her comment pointed to an out-and-out error, fix it forthwith, and be glad of the public embarrassment she saved you. If on the other hand you used the word purposefully and creatively, and because no other English word delivers the right shade of meaning, your editor might be holding you back in the venerable art of word invention. Children’s literature is full of made-up words, because children reach beyond their vocabularies all the time to amusing—and often revealing—effect. A page torn from the linguistic annals of my grandchildren: commenting on his older brother Liam’s behavior, three-year-old Levi borrowed from his mother’s sense of right and wrong when he said, "That’s not a-poopie-ate, right mommy?" I say we wordsmiths can learn from their fearlessness. The world of language would be less fanci...