Meaning/Usage: To forget something that you had to do

Explanation: When you "slip," you fall. When it falls from the mind, it is no longer there. So when you forget about something, it is common to say, it "slipped my mind."

"I was meaning to call you but it totally slipped my mind."
"There was something I needed to do today but it totally slipped my mind."
"Sorry I forgot about your birthday. It totally slipped my mind."

A. "Did you call your mom and dad and wish them Happy Anniversary?"
B. "Oh no! It totally slipped my mind."

Other Common Sentences

"I completely forgot."