- A word, phrase, or sentence that has the property of forming another word, phrase, or sentence when its letters are reversed. A semordnilap differs from a palindrome in that the word or phrase resulting from the reversal is different from the original word or phrase.
A reverse spelling of palindromes. "Semordnilap," according to author O.V. Michaelsen, was probably first used by recreational linguist Dmitri Borgmann, cited by Martin Gardner in the revised edition of C. C. Bombaugh's Oddities and Curiosities of Words and Literature (1961) . The underlying concept (but not the term) is found at least as far back as Lewis Carroll's Sylvie and Bruno (1889).