Row with subordinate causes stress (9)
I believe the answer is:
underline
'stress' is the definition.
(I know that underline is a more specific form of the action stress)
'row with subordinate' is the wordplay.
'row' becomes 'line' (as in a row of things).
'with' is a charade indicator (letters next to each other).
'subordinate' becomes 'under' (similar in meaning).
'line' after 'under' is 'UNDERLINE'.
'causes' is the link.
(Other definitions for underline that I've seen before include "Form of emphasis in writing" , "Method of showing emphasis in writing" , "Emphasize, stress importance" , "Call attention to - highlight" , "Reinforce" .)