Mark follows old man (5)
I believe the answer is:
oscar
'man' is the definition.
(I've seen this before)
'mark follows old' is the wordplay.
'mark' becomes 'scar' (synonyms).
'follows' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'scar' after 'o' is 'OSCAR'.
(Other definitions for oscar that I've seen before include "One close to Mike" , "Comms code for "O"" , "Cinema award" , "Phonetic code for O" , "Librettist Hammerstein, d. 1960" .)