cloud是“云朵”，nine是“九”，on cloud nine可不是在第九朵云上，而是乐不可支；极为快乐。

【例句】
He was on cloud nine after his wife had the baby.
他因为妻子生了小宝宝而心里乐开了花。

After the promotion in her company, she's on cloud nine.
在公司升职后，她高兴极了。