Pil (placename)

Pîl (also rendered as Pill, Pil or Pyll) is a Welsh placename element. The name is defined as the tidal reach of a waterway, suitable as a harbour, but is only common along the Bristol Channel and Severn Estuary. The highly localised distribution suggests it may have only been applicable to waterways within the tidal reach of the Severn sea.
The name is today most commonly associated with the village of Pyle in Glamorgan, and the small village of Pill in Somerset.
Usage.
In toponymy and hydronymy the word is often mistaken for another Welsh word "Pŵll" ("Pool"), however there is no proven link between the words and the two are often found within the same localities (for example, medieval Caerleon had a "Pwll Mawr" and a "Pîl Mawr" either side of the Roman port). Pîl may have developed a secondary meaning of 'refuge', as the name appears in some inland areas (such as Pilleth in Powys).
Although the name is associated with the coastline of Glamorgan and Gwent, it is found on both sides of the Severn, from Pembrokeshire in the west to Somerset and Gloucestershire in the East. In South West England, the word is rendered as Pill, and is interpreted by Robert Macfarlane as denoting "a tidal creek or stream...capable of holding small barges". Rick Turner noted the word as part of a common lexicon, shared across the Gwent, Somerset and Gloucestershire Levels.
History.
The predominance of "Pîl" in the area is an indication of their importance to the local maritime culture, especially along the river Usk where Pîls are found at the old Roman port in Caerleon and the later city of Newport. 
Newport developed around a number of Pîls, such as those at Pillgwenlly, said to have been the base of piracy by Gwynllyw (the future patron saint of Newport, it's Cathedral and pirates) and Arthur's Pîl (or Town Pîl), the site of the 2002 archaeological discovery of the Newport ship (now the Riverfront Arts Centre).