Meaning:

Cannot remember something such as a word or the name of a person although you think you know it and you will remember it soon.

If you say something is on the tip of your tongue, you mean you can almost remember it but not right away.

Example: What's the girl's name there?
Wait a second, it's on the tip of my tongue. ... Yes! Her name is Joanne.

The teacher asked them a question. The answer was on the tip of his tongue, but another student raised her hand and said it first.

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