Period Queen Anne initiated (3)
I believe the answer is:
era
'period' is the definition.
(era is a kind of period)
'queen anne initiated' is the wordplay.
'queen' becomes 'er' (abbreviation for Elizabeth Regina**).
'initiated' says to take the initial letters.
The first letter of 'anne' is 'a'.
'er'+'a'='ERA'
(Other definitions for era that I've seen before include "Long historical period" , "Distinct period in history" , "Are involved in time span" , "Important time" , "Characteristic period" .)