A canvas bag that is used to feed an animal (such as a horse); covers the muzzle and fastens at the top of the head WordNet 3.0 & Open English WordNet

A feedbag, feed bag, feeding bag, nosebag, or morral, is a bag, filled with fodder, and attached to the head of a horse, enabling it to eat. Wikipedia

A horse's nosebag. Wiktionary

A round sack or bag to feed for a horse, mule, ox or alike animal. Usually made of canvas sides and leather bottom slipped over the nose and attached to harness my a strong strap, rope or string. Design to feed animal in public areas and to eliminate spillage from eating. Wiktionary

A round sack to feed an animal. Wiktionary (translation)