folk etymology

noun2

1. •
   A popular explanation for the origin of a term which has been rejected as false by expert etymologists.

   • Many English folk etymologies involve backronyms.
   • The spelling in 'sovereign' was influenced by folk-etymology association with 'reign'.
2. •
   A modification of a word or its spelling resulting from a misunderstanding of its etymology, as with island, belfry, and hangnail.