(noun) - 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 must be different from the original word or phrase.
See my list Dyslexic's Dread for a whole bunch of these.
Interesting info on it here. Also see ambigram.
(noun) - 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 must be different from the original word or phrase.