on the tip of your tonguea) if something is on the tip of your tongue, you really want to say it, but then you decide not to 话到嘴边，想说而未说的 It was on the tip of my tongue to say, ‘I’d rather have dinner with a snake.’ 我已经话到嘴边:“我宁愿和一条蛇共进晚餐。”
b) if a word, name etc is on the tip of your tongue, you know it but cannot remember it 就在嘴边〔但想不起来了〕 What is her name? It’s on the tip of my tongue. Joan. Joan Simpson. That’s it! 她叫什么？就在我嘴边。琼——琼•辛普森。就是这名字！
→ on the tip of your tongue at tip1(2)