Charles and Mike in 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'
'in' acts as a link.
(Other definitions for chasm that I've seen before include "Wide difference" , "Deep hole" , "Pit" , "Wide gap" , "Great divide" .)