Time of derangement (3)
I believe the answer is:
era
'time' is the definition.
(I know that era is a type of geologic time)
'of derangement' is the wordplay.
'of' indicates a hidden word.
'ERA' can be found hidden inside 'derangement'.
(Other definitions for era that I've seen before include "Period, age" , "Significant time" , "Period of alteration" , "Aeon" , "Long historic period" .)