Ralph Dunstan, D. Mus, a Cornishman, published the Dilly Carol in 1923 in his "First Book of Christmas Carols" (don't know if he ever got round to producing a second). He noted "The mythical Dilly bird was supposed to come only at Christmas but was 'never seen but heard-o'. Variants of the dilly Carol are sung in most countries of Europe. The [version in my book] is exactly as I have many times heard it - generally sung by three singers at or about the time of Twelfth Night - in West Cornwall ..."

I have a theory that "dilly" is relatyed to the Welsh word "dilys" which is both a personal name and also means "true, authentic" (as far as I know). I have heard somewhere that it once meant "excellent". Are there any Welsh or Cornish speakers who can confirm this, or at least comment?