Charles and Mike in a terrible hole! (5)
I believe the answer is:
chasm
'terrible hole' is the definition.
'chasm' can be an answer for 'hole' (I have seen 'Deep hole' mean 'chasm' so perhaps 'hole' could also mean 'chasm'). I am unsure of the 'terrible' bit.
'charles and mike' is the wordplay.
'charles' becomes 'Chas' (shortened form).
'and' is a charade indicator (letters next to each other).
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'chas'+'m'='CHASM'
'in a' acts as a link.
Can you help me to learn more?
(Other definitions for chasm that I've seen before include "Gaping hollow" , "Gorge" , "Yawning gap" , "Deep opening in the earth's surface" , "What's split" .)