Complete from beginning to end, concealing nothing (8)
I believe the answer is:
thorough
'complete' is the definition.
('thorough' can be similar in meaning to 'complete')
'from beginning to end concealing nothing' is the wordplay.
'from beginning to end' becomes 'through' (I've seen this before).
'concealing' is an insertion indicator.
'nothing' becomes 'o' (looks like zero - 0).
'through' going around 'o' is 'THOROUGH'.
(Other definitions for thorough that I've seen before include "Miticulous or exhaustive" , "'Exhaustive, complete (8)'" , "Attentive to detail" , "Full" , "Meticulous - exhaustive" .)