Chap almost challenging high-ranking bureaucrat (8)
I believe the answer is:
mandarin
'high-ranking bureaucrat' is the definition.
(I've seen this before)
'chap almost challenging' is the wordplay.
'chap' becomes 'man' (I've seen this before).
'almost' means to remove the last letter (most of the word but not all of it).
'challenging' becomes 'daring' (daring is a kind of challenging).
'daring' with its last letter removed is 'darin'.
'man'+'darin'='MANDARIN'
(Other definitions for mandarin that I've seen before include "Form of Chinese" , "High-ranking bureaucrat" , "Top person in Whitehall" , "Drain man (anag) - high-ranking Chinese official" , "Reddish-orange, loose-skinned citrus fruit" .)