For those have read The Adventures of Tom

[Huinesoron]

Originally Posted by Inziladun

Indeed. "Tom" is a nickname for "Tolman" in the Shire, and it would seem that "Tom" was common enough in Shire usage for it to be the name given by the local hobbits to the odd person living on their eastern border.
Whence "Bomdadil", though?

By the conceit of translation, 'Bombadil' must be Tolkien's cod-Middle-English translation of the true Hobbitish name given to Iarwain Ben-adar. It could, of course, be an untranslatable nonsense-name (as Took), but - especially in light of the fact that he at one point calls himself 'Tom Bombadillo' - it seems entirely plausible that the Shire-folk created it from the Hobbitish Westron words for 'bombast' and 'peccadillo'. In other words: he's loud, he's weird, and there's something just a little bit wrong with him.

hS