Ten-year span (6)
I believe the answer is:
decade
'ten-year span' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for decade that I've seen before include "The 1960s, for example" , "Tenth of a century" , "The noughties maybe" , "Ten year period" , "Period of ten years" .)