n.close-fitting conical cap worn as a symbol of liberty during the French Revolution and in the U.S. before 1800
英汉双解大词典
liberty cap
1.
N（名词）
a cap of soft felt worn as a symbol of liberty, esp during the French Revolution, from the practice in ancient Rome of giving a freed slave such a cap 自由帽; 一种代表自由的软帽，古罗马时代给予获得自由的奴隶，法国革命时戴此帽以示自由