BONNET  (from

Lat. bonetum, a kind of stuff, then the cap made of this stuff), originally a soft cap or covering for the head, the common term in English till the end of the 17th century; this sense survives in Scotland, especially as applied to the cap known as a " glengarry." The " bonnet " of a ship's sail now means an additional piece laced on to the bottom, but it seems to have formerly meant a piece laced to the top, the term " to vail the bonnet " being found at the beginning of the 16th century to mean "strike sail" (from the Fr. avaler), to let down . In modern times " bonnet " has come to be used of a type of head-covering for women, differentiated from " hat " by fitting closely to the head and often having no brim, but varying considerably in shape according to the period and fashion . The term, by a natural extension,, is also applied to certain protective devices, as in a steam-engine or safety-lamp, or in slang use to a gambler's accomplice, a decoy .