A word such as CIVIC, ROTATOR, or SEMITIMES, that is spelled exactly the same way backward as it is forward, is called a palindrome. There are many short palindromes, but the number decreases sharply with increase in word length.
Borgmann, Dmitri A.
"The Evolution of a Palindrome,"
Word Ways: Vol. 3
, Article 3.
Available at: http://digitalcommons.butler.edu/wordways/vol3/iss1/3