Charlie, cleaner, in mountaineering challenge (4)
I believe the answer is:
crag
'mountaineering challenge' is the definition.
(I've seen this in another clue)
'charlie cleaner' is the wordplay.
'charlie' becomes 'C' (phonetic alphabet: alpha, bravo, charlie etc.).
'cleaner' becomes 'rag' (I can't justify this - if you can you should believe this answer much more).
'c'+'rag'='CRAG'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for crag that I've seen before include "Steep rugged rock or cliff" , "Steep or rugged cliff face" , "Steep rocky cliff" , "Avant-garde" , "Steep, rugged peak" .)