'Whiskey in the Jar' is also known as 'Kilgarry Mountain'...

'The Rout of the Blues' is sometimes called 'Scarborough Sands' because one version mentions Scarborough Sands in the first line, though the version I learned had 'Salisbury Plain'...

People often have their own pet name for a song, which is often the first line of the first verse, the chorus or refrain, but, as others have suggested, could be anything at all!!

Then, of course, we have names of tunes... how on earth did anyone come up with 'Pull out the knife and stick it in again'...??!!