Mark finds mine's cool, somehow (9)
I believe the answer is:
semicolon
'mark' is the definition.
(I know that semicolon is a type of punctuation)
'mine's cool somehow' is the wordplay.
'somehow' indicates an anagram.
'mines'+'cool'='minescool'
'minescool' anagrammed gives 'SEMICOLON'.
'finds' acts as a link.
(Other definitions for semicolon that I've seen before include "half a stop" , "Punctuation mark denoting a pause in a sentence" , "used by writers for a break" , "Joiner" , "can cut sentence" .)