The two nouns are pretty much synonymous. However, if you hear a piece of music that you like you would probably say that it's a good tune. If you said you like the melody then you would probably be referring to the main part of a harmony.
Assuming that this page looks similar to you as it does to me, there's a line nearly at the top of the page that says:Dictionary and thread title search:
If your default forum language is not English, it might be in another language. If you enter the work in the text box provided and click on the submit button, which is called "search" in English, you will be taken not only to the WRD defintion, but to a list of threads with that word in the title.
Additionally, there is a "search" option further down the page that will search the contents of posts as well.