Absolute straightforwardness putting outsiders off (8)
I believe the answer is:
implicit
'absolute' is the definition.
(similar in meaning)
'straightforwardness putting outsiders off' is the wordplay.
'straightforwardness' becomes 'simplicity' (simple can mean straightforward or easy).
'putting outsiders off' says to take the centre (outside letters are removed).
The centre of 'simplicity' is 'IMPLICIT'.
(Other definitions for implicit that I've seen before include "Suggested indirectly" , "Latent, unexpressed" , "Unspoken" , "Absolute and unquestioning, as obedience should be" , "Suggested but not stated" .)