tinfoil hat

English Wikipedia has an article on:

tinfoil hat

Wikipedia

• tin-foil hat, tin foil hat
• TFH (initialism)

From tinfoil +‎ hat.

tinfoil hat (plural tinfoil hats)

1. A piece of headgear made from one or more sheets of tin foil, aluminium foil, or other similar material, especially when worn in the belief that it shields the brain from electromagnetic fields, or against mind control or mind reading.
   • 1916, Roger W Allen, editor, Millinery Trade Review, volume 41, page 27:

     Jeanne Due's ingenuity has sent the most remarkable of hats, this being the now notorious tinfoil hat, pictured elsewhere. The strangest part about this weird creation, however, is the fact that it is not unbecoming, but quite wearable.

   • 2001, Eoin Colfer, Artemis Fowl, page 42:

     To prevent them from reading his mind, he wore a tinfoil hat at all times.

   • 2008, Libby Sternberg, Recovering Dad, page 27:

     I mean, as much as any daughter, I want to make sure my mother is headed for happiness and not heartbreak, but Connie's taken it up a notch, to tinfoil-hat territory.

   • 2021 March 23, David Von Drehle, “Sidney Powell does an about-face on her Stop the Steal claims”, in Washington Post‎^[1], →ISSN:

     It’s true that Team Trump, and its cowering minions in Congress, eventually parted ways with Powell as her professional demeanor gradually slipped to reveal her tinfoil hat.

2. (by extension) A conspiracy theorist.

• tinfoil hatter
• tinfoilhattery