Horribly proud, about to have great fall (8)
I believe the answer is:
downpour
'great fall' is the definition.
'downpour' can be an answer for 'fall' (I have seen 'Big fall' mean 'downpour' so perhaps 'fall' could also mean 'downpour'). I am not sure about the 'great' bit.
'horribly proud about to have' is the wordplay.
'horribly' indicates an anagram (a horribly wrong version of the letters).
'about' is an insertion indicator.
'to have' becomes 'own' (to have something is to own it).
'proud' with letters rearranged gives 'dpour'.
'dpour' enclosing 'own' is 'DOWNPOUR'.
Can you help me to learn more?
(Other definitions for downpour that I've seen before include "Deluge" , "Heavy fall of rain" , "Big fall makes" , "cats and dogs?" , "Cloudburst" .)