1492 and 1776 (5)
I believe the answer is:
years
'1492 and 1776' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for years that I've seen before include "Long periods" , "Ages" , "Measures of time" , "Very long time (colloq.)" , "Periods of time" .)