What is the term for a word which is another word spelled backwards?
There's no generally accepted term. The simplest way of referring to such words (e.g. lap/pal, dog/god) is probably semi-palindrome or half-palindrome. Some other suggestions have been made, including heteropalindrome, reversgram (or reversible anagram), and semordnilap (i.e. palindromes written backwards).
See other Vocabulary Questions.
Take a look at: What is the term for a word that has two opposite meanings?
We take a look at several popular, though confusing, punctuation marks.