semordnilap

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).

semordnilap (plural semordnilaps)

1. 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.
   • 1965, Dmitri Borgmann, Language on Vacation: An Olio of Orthological Oddities‎, page 42:

     [he] then goes on to credit us with giving him some of the best examples of semordnilaps.

   • 2000, Gail Smith, Celebrate the Piano, page 18:

     This song is a semordnilap. It can be played forward and then sounds different when it is played backwards.

   • 2008, Alex Pogel & David Ozonoff, “Contingency Structures and Concept Analysis”, in Medina & Obietkov, editors, Formal Concept Analysis, page 318:

     ACE is an acronym for Analysis of Concepts for Epidemiologists, and a semordnilap for ECA, Epidemiological Concept Analysis.

• (word, phrase, or sentence that forms another when its letters are reversed): anadrome, half-palindrome, heteropalindrome, reversgram, reversible anagram, semi-palindrome, word reversal, levidrome
• See also antigram, in which the meaning is necessarily negated but letters may be freely rearranged.

• palindromes