A napron became an apron: the n crossed the word boundary.
Nape produced the smaller-cloth formation naperoun. English received forms including napron. When a napron was redivided as an apron, the n moved across the word boundary. The garment name now hides its relationship to napkin.
These are selected forms; spellings and protective-cloth uses overlapped. The deeper Latin history is omitted.
Source
Merriam-Webster: apronWord History identifies nape, naperoun and the English redivision; its note qualifies the early cloth senses.