Antique dickey, made of starched linen. Tenax shirt front, style number 5. Probably Edwardian.
This type of garment was popular because it saved having to have your shirt washed and starched every day - and it was small enough to be laundered and starched at home. Length (straight down the front) 11 inches. Maximum width (not counting the neckband) 10.5 inches.
Condition: Antique dickey front, over a century old and rather past its heyday. Quite heavy storage marks (scuffs and age spots). The top stud hole has been torn, as shown. I don't think it would clean up well enough to wear, but might come in useful as a historical garment! Previous owner's name and laundry mark on the bottom of the bib.