I agree with Faldage--I think the writer is referring to the concept the word stands for, not the word itself. In this sense, I strongly disagree with 'birth'--it's nasty and disgusting. (I'd have been a good candidate to be an adoptive mom.) Ew.
If we're talking about sound, I'd still vote for mellifluous. We had a thread or two here some time ago on this kind of thing.
If we're talking about the way a word looks, my first thought was 'mellow' because it is tall only in the middle; but I think most palindromes would be better, as they are perfectly balanced.