1.nounA word, phrase, number or any other sequence of units which has the property of reading the same forwards as it does backwards, character for character, sometimes disregarding punctuation, capitalization and diacritics.
"Level, madam and racecar are examples of single word palindromes."
2.noun(by extension) A poetic form in which the sequence of words reads the same in either direction.
3.nounA stretch of DNA in which the sequence of nucleotides on one strand are in the reverse order to that of the complementary strand