The term OPERA HAT is used to describe a type of hat that is typically worn to the opera. The two crossword solutions for this term are GIBUS (5 letters) and TOPPER (6 letters). A GIBUS is a type of collapsible top hat that was popular in the 19th century, while a TOPPER is a more modern version of the same style of hat. Both of these hats are typically associated with formal occasions such as the opera.