diaper: [14] The notion underlying diaper is of extreme whiteness. It comes ultimately from Byzantine Greek díaspros, which was a compound formed from the intensive prefix diaand áspros ‘white’. (Aspros itself has an involved history: it started life as Latin asper ‘rough’ – source of English asperity – which was applied particularly to bas-relief on carvings and coins; it was borrowed into Byzantine Greek and used as a noun to designate silver coins, and their brightness and shininess led to its reconversion into an adjective, meaning ‘white’.) Díaspros appears originally to have been applied to ecclesiastical vestments, and subsequently to any shiny fabric.
When the word first entered English, via medieval Latin diasprum and Old French diapre, it referred to a rather rich silk fabric embellished with gold thread, but by the 16th century it was being used for less glamorous textiles, of white linen, with a small diamond-shaped pattern. The specific application to a piece of such cloth used as a baby’s nappy (still current in American English) seems to have developed in the 16th century. => asperity
