Figure pathogen out (8)
I believe the answer is:
heptagon
'figure' is the definition.
(heptagon is a kind of figure)
'pathogen out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'pathogen' anagrammed gives 'HEPTAGON'.
(Other definitions for heptagon that I've seen before include "A geometric figure with seven sides" , "Seven-sided object" , "Seven-sided figure" , "Seven-sided shape" .)