The name of this well-known spot, in common with many other names of coastal features, does not occur in the early written records. It first appears on the first edition of the Ordnance Survey map, dated 1811, spelt Dirdale Door
. Other spellings on early 19th-century maps include Duddledoor
(1825) and Durdle or Dudde Door
The final Door is easy, since it clearly refers to the arch of rock projecting into the sea. But the first part of the name, almost certainly much older, is more difficult to explain in the absence of early spellings. However, on the analogy of other similar names which do have such spellings, it is possible to conjecture that it may be from an Old English word thyrelod 'pierced, having a hole'.
The Dorset names Durlston Bay and Head (in Swanage) and Durdle Pier (in Portland), again without early spellings, can be associated etymologically with Durdle Door. Durlston appears with that spelling from only 1774, but almost certainly means 'rock with a hole in it' from Old English thyrel 'hole, having a hole' and stan 'stone or rock'
. This is thus an exact doublet of Thurlestone in Devon, which is on record from as early as the 9th century. Durdle Pier, recorded only from the 18th century, is likewise probably identical in origin with Durdle Door.http://www.thedorsetpage.com/locations/Place/...