Pure speculation, but an apron (or 'a napron' if you prefer) is (or was) a very personal item, compared with a napkin which is usually part of a large set of si

Pure speculation, but an apron (or 'a napron' if you prefer) is (or was) a very personal item, compared with a napkin which is usually part of a large set of similar-to-identical items. So the expression 'mine napron' (hard to say) becomes 'mine apron' (easy to say). Whereas people weren't possessive about napkins. Trivia: British English gets the word 'nappy' from 'napkin', whereas the American English 'diaper' comes from the type of fabric from which the 'napkin' was made