palindrome
noun [ C ] uk/ˈpæl.ɪn.drəʊm/ us/ˈpæl.ɪn.droʊm/
回文（顺读和倒读都一样的词、诗句等）
a word or group of words that is the same when you read it forwards from the beginning or backwards from the end
"Refer" and "level" are palindromes. refer 和 level 是回文词。