Several periods are given up
I believe the answer is:
era
'several periods' is the definition.
(I've seen this in another clue)
'are given up' is the wordplay.
'given up' shows that the letters should be reversed in order (in a down clue, letters go up).
'are' backwards is 'ERA'.
(Other definitions for era that I've seen before include "Cycle" , "Significant time" , "Special time" , "Epoch, period" , "Age marked by a distinctive character" .)