Complete, from beginning to end, hiding nothing (8)
I believe the answer is:
thorough
'complete' is the definition.
('thorough' can be similar in meaning to 'complete')
'from beginning to end hiding nothing' is the wordplay.
'from beginning to end' becomes 'through' (I've seen this before).
'hiding' is an insertion indicator.
'nothing' becomes 'o' (looks like zero - 0).
'through' enclosing 'o' is 'THOROUGH'.
(Other definitions for thorough that I've seen before include "Miticulous or exhaustive" , "Doing things with great attention to detail" , "Leaving no stone unturned" , "Assiduous, painstaking" , "Total - painstaking - in-depth" .)