Obvious answer pages are not vacuous (8)
I believe the answer is:
apparent
'obvious' is the definition.
('apparent' can be similar in meaning to 'obvious')
'answer pages are not vacuous' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'pages' becomes 'pp'.
'vacuous' means to remove the middle letters.
'not' with its centre taken out is 'nt'.
'a'+'pp'+'are'+'nt'='APPARENT'
(Other definitions for apparent that I've seen before include "Conspicuous" , "Quite obvious and clear" , "See 1" , "Obvious; seemingly true" , "cut , book written on a page" .)