Part of another age or epoch (3)
I believe the answer is:
era
'epoch' is the definition.
(I know that epoch is a class)
'part of another age or' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'ERA' can be found hidden inside 'another age or'.
(Other definitions for era that I've seen before include "Geological age" , "Important time" , "Distinctive period of time" , "quite some time" , "Important historical period" .)