Mark and Edward worried (6)
I believe the answer is:
scared
'worried' is the definition.
(I've seen this in another clue)
'mark and edward' is the wordplay.
'mark' becomes 'scar' (mark left by an injury).
'and' is a charade indicator (letters next to each other).
'edward' becomes 'Ed' (short for Edward).
'scar'+'ed'='SCARED'
(Other definitions for scared that I've seen before include "Frightened or intimidated" , "Fearful, anxious" , "Frightened, alarmed" , "Frightened or apprehensive" , "Thing which precipitates an event" .)