Haughty answer to diatribe about capital's rate of growth (8)
I believe the answer is:
arrogant
'haughty' is the definition.
(I've seen this before)
'answer to diatribe about capital's rate of growth' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'to diatribe' becomes 'rant' (I've seen this in other clues).
'about' is an insertion indicator.
'capital' indicates taking the first letters.
The first letters of 'rate of growth' is 'rog'.
'rant' going around 'rog' is 'rrogant'.
'a'+'rrogant'='ARROGANT'
(Other definitions for arrogant that I've seen before include "Overbearingly proud" , "Proud and overbearing, feeling superior" , "Overbearing; conceited" , "Over-cocky" , "High and mighty" .)