n. 1 a a woman's or child's hat tied under the chin and usu. with a brim framing the face. b a soft round brimless hat like a beret worn by men and boys in Scotland (cf. TAM-O'-SHANTER). c colloq. any hat. 2 Brit. a hinged cover over the engine of a motor vehicle. 3 the ceremonial feathered head-dress of an American Indian. 4 the cowl of a chimney etc. 5 a protective cap in various machines. 6 Naut. additional canvas laced to the foot of a sail. bonnet monkey an Indian macaque, Macaca radiata, with a bonnet-like tuft of hair. bonneted adj.
[ ME f. OF bonet short for chapel de bonet cap of some kind of material (med.L bonetus) ]