have no recollection of something to be completely unable to remember something, so that you think that perhaps it never happened: I have absolutely no recollection of ever seeing this man.
slip your mind if something slips your mind, you forget it because you are busy doing other things: I’m sorry I didn’t phone, I was working and it slipped my mind.
be on the tip of your tongue used for saying that you cannot remember a name or fact that you know, but that you think you will remember it soon: What was his name again? It’s on the tip of my tongue.
my mind’s gone blank used for saying that you cannot remember something, especially when someone has asked you a question: When he asked me her name, my mind just went blank.
blank (out) an informal expression meaning to unexpectedly be unable to remember something: I totally blanked when it came to the written part of the exam.
draw a blank to be completely unable to remember something you ought to know: Students forget information they know they studied, become confused about things they thought they knew, and may draw a complete blank.
Language tip of the week: forget | Macmillan