Chapeau

Cap of Estate, Cap of Dignity, Cap of Honour, Cap of Maintenance, Cap of State, Capeline, Capelot, Duciper 

Anciently belonging to the dignity of duke, it is formed of crimson velvet turned up ermine and most commonly called a chapeau. It is often borne under the crest instead of a wreath.

Chapeau de fer is an iron hat with a small brim, resembling the morion used by foot soldiers. 

The Cap of  Maintenance, or of State, as borne by the Lord Mayor of the City of London is of brownish fur.