Pass on to a punctuation mark (5)
I believe the answer is:
colon
'to a punctuation mark' is the definition.
(colon is a kind of punctuation mark)
'pass on' is the wordplay.
'pass' becomes 'col' (col is a term for a mountain pass).
'col'+'on'='COLON'
(Other definitions for colon that I've seen before include "cut short dependency?" , "cash" , "City at the Caribbean entrance to the Panama Canal" , "Part of body; some punctuation" , "Start of one canal" .)