Period of British history from 1811 to 1820 (7)
I believe the answer is:
regency
(Other definitions for regency that I've seen before include "Interim ruling period on behalf of another" , "Period (1811-20) covering The Madness of King George III" , "Late eighteenth century to early nineteenth century style" , "Style of British furniture, architecture, etc" , "historical period" .)