Throughout (6)
(Other definitions for across that I've seen before include "Clue with solution not going in the direction of this one!" , "...this is 'Number Ten'" , "Transverse" , "Facing" , "ax" .)
'throughout' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for during that I've seen before include "Throughout the time of" , "Concurrently" , "Throughout or at a point in the continuance of" , "In the course of" .)