ageing From wiki
"According to a 1975 edition of the Mariner's Mirror, the term pea coat originated from the Dutch or West Frisian word pijjekker or pijjakker, in which pij referred to the type of cloth used, a coarse kind of twilled blue cloth with a nap on one side.[10]"
"Another theory, favoured by the US Navy, is that the heavy topcoat worn in cold, miserable weather by seafaring men was once tailored from "pilot cloth" – a heavy, coarse, stout kind of twilled blue cloth with the nap on one side. This was sometimes called P-cloth from the initial letter of pilot, and the garment made from it was called a P-jacket – later a pea coat. The term has been used since 1723 to denote coats made from that cloth.[11]"
I went down a very interesting wiki fashion hole for a good half hour there. 