1. To leave a scar (in place of some wound) after healing. Thankfully the incision isn't very noticeable after it scarred over. That cut is going to scar over if you don't stop picking at that scab!
2. Of some painful event, to stop hurting in one's heart, especially in a way that does not confront or resolve the painful emotions. Just when I think the death of my daughter has finally started to scar over, that I'll finally stop grieving every second of every day, something reminds me of her and the pain comes rushing back as intense as ever. His broken heart eventually scarred over, but it left him cold and distrustful of ever giving his love so fully to anyone ever again.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
[for an injury] to form and leave a scar. The wound will scar over, but your arm will never be the same as it was before the accident.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.