Big band ___ (3)
(Other definitions for era that I've seen before include "Specific time" , "Characteristic period" , "Series of years" , "Stage" , "Long period of history" .)
'big band' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for horde that I've seen before include "lots of people" , "Large force" , "Nomadic army" , "Migratory tribe; army" , "Host" .)