Eccentricity of Foreign Office manual lacking introduction (6)
I believe the answer is:
foible
'eccentricity' is the definition.
(I have seen 'Minor eccentricity ' mean 'foible' so perhaps 'eccentricity' could also mean 'foible')
'foreign office manual lacking introduction' is the wordplay.
'foreign office' becomes 'FO' (abbreviation).
'manual' becomes 'bible'.
'lacking introduction' means to remove the first letter.
'bible' with its initial letter taken away is 'ible'.
'fo'+'ible'='FOIBLE'
'of' is the link.
(Other definitions for foible that I've seen before include "Quirk" , "'Mannerism, idiosyncrasy (6)'" , "Harmless peculiarity or mannerism" , "Harmless peculiarity in person's character" , "Minor eccentricity" .)