In his 1955 valedictory address English and Welsh, J.R.R. Tolkien mentioned cellar door as a combination of English words having an especially beautiful sound independent of their meaning (i.e. purely phonaesthetically beautiful):
Most English-speaking people ... will admit that cellar door is 'beautiful', especially if dissociated from its sense (and from its spelling). More beautiful than, say, sky, and far more beautiful than beautiful. Well then, in Welsh for me cellar doors are extraordinarily frequent, and moving to the higher dimension, the words in which there is pleasure in the contemplation of the association of form and sense are abundant.
Because of this speech Tolkien is one of several prominent writers and linguists to whom the phrase is erroneously attributed. In fact the 'cellar door' aphorism was in circulation for at least fifty years before Tolkien used it – the first published instance being in a 1903 novel Gee Boy by Cyrus Hooper, and even there it is implied the phrase came from another source.
- Cellar door at Wikipedia.