Charles and Mike split (5)
I believe the answer is:
chasm
'split' is the definition.
(thesaurus)
'charles and mike' is the wordplay.
'charles' becomes 'chas' (shortened form).
'and' says to put letters next to each other.
'mike' becomes 'm' (phonetic alphabet: alpha, bravo, charlie etc.).
'chas'+'m'='CHASM'
(Other definitions for chasm that I've seen before include "Abyss" , "big break?" , "Deep opening in the earth's surface" , "Yawning gap" , "Wide difference" .)