Once a common type of headwear for both men and women, bonnets have more recently become appropriate only for babies. Over time, bonnets have changed shape drastically and the meaning of the word itself has become much more specialized.
Originally, "bonnet" was the name given to any kind of men's headwear. By the eighteenth century, it delineated an enormous hat worn only by nobles. This type of hat was very lacy and frilly, and may have been made of ermine or velvet. Near the end of the eighteenth century, bonnets took on a more specific shape, usually featuring a brim that jutted out from the forehead and continued down the sides of the face.
In nineteenth century England, the word "bonnet" eventually took on the meaning of a woman's head covering, which was worn outdoors in public places to cover the hair. The shape of the hat continued to become more specific and the peak or brim larger, sometimes so large that it actually restricted all peripheral vision for the wearer. Women would wear different bonnets for summer, which were usually made of straw, and winter, which were made of a heavier fabric. Easter was the time designated as the first day to wear one's summer bonnet, hence the "Easter Bonnet Parade."
There was a definite distinction between the bonnets of upper-class women and those of the lower-class. "Slat bonnets," for example, were worn by rural women, and featured a shallower brim and a curtain that hung down from the back of the hat to cover the upper shoulders. "Poke bonnets" were more fashionable and were often worn by upper-class women. They featured a large, wide brim and were trimmed with ribbons, frills or flowers.
As times changed and it became appropriate for women to show their hair in public, bonnets died out as a mainstay for women's outdoor wear. In contemporary times, bonnets are generally only worn by babies. The baby bonnet is usually made of a soft, knitted material which ties just under the chin. It covers the hair and ears of the baby to keep them warm in cold weather. In the military, however, men's headwear is still sometimes known as a bonnet, such as glengarry bonnets, which are boat-shaped military caps.