Key is with lock in Harrow (8)
I believe the answer is:
Here is my best explanation:
'harrow' is the definition.
'key is with lock' is the wordplay.
'key' becomes 'd' (I've seen this in other clues**).
'with' says to put letters next to each other.
'lock' becomes 'tress' (I've seen this before).
'in' is the link.
(Other definitions for distress that I've seen before include "Psychological suffering", "Sadden", "Mayday is such a signal.", "Affliction", "Extreme anxiety or sorrow", "Feeling of anxiety or suffering", "Extreme sorrow or pain", "Upset", "Deep anxiety" and "Such a signal indicates trouble".)