if something slips your mind memory , you forget to do it
How could she have let something so important slip her mind?
Thesaurus: to forget, or to try to forgetsynonym
Main entry: slip
* * *
slip your ˈmind idiom
if sth slips your mind, you forget it or forget to do it
•
I'm sorry I didn't tell you. It completely slipped my mind.
Useful english dictionary. 2012.