motte and bailey

noun2

1. •
   The predecessor of the European castle, having a raised earth mound (the motte) topped with a tower (or donjon), and a wooden ring fortification surrounding a courtyard (the bailey).

   • Deepwood is a motte-and-bailey castle in the midst of thick forest, easy to creep up on unawares. A wooden castle, defended by an earthen dike and a palisade of logs. — 2011
2. •
   (rhetoric) A form of argument and an informal fallacy where an arguer conflates two similar positions, one modest and easier to defend (the "motte") and one much more controversial (the "bailey"), by advancing the controversial position, but when challenged, insisting that they are only advancing the more modest position.