Public knowledge covering area passed (9)
I believe the answer is:
overtaken
'passed' is the definition.
('overtake' can be a synonym of 'pass')
'public knowledge covering area' is the wordplay.
'public' becomes 'overt' ('overt' is associated in meaning with 'public').
'knowledge' becomes 'ken' (ken is a kind of knowledge**).
'covering' means one lot of letters goes inside another.
'area' becomes 'a' (maths abbreviation).
'overt'+'ken'='overtken'
'overtken' enclosing 'a' is 'OVERTAKEN'.
(Other definitions for overtaken that I've seen before include "Passed on road" , "left behind" .)