A hat with a broad brim that protects the face from direct exposure to the sun WordNet 3.0 & Open English WordNet

A sun hat is any hat or headgear specifically designed to shade the face, neck and shoulders from direct sunlight, usually with a circumferentially-protruding semi-rigid brim that can range from small to large, but as a general guideline around 4 to 7 in in width. Wikipedia

Wide-brimmed hat designed to shade face and shoulders from the sun Wikidata

A light, wide-brimmed hat to protect from the sun. Wiktionary

A hat to protect from the sun. Wiktionary (translation)