In British English, nelly turns up in the set phrase not on your nelly, which means you are definitely not going to do something — a firm, colourful no. It is informal and a bit old-fashioned; you hear it from older British speakers more than from young ones, often with a laugh.

In British English在英式英文裡，nellynelly這個字 turns up in the set phrase會出現在固定用語 not on your nelly「not on your nelly」裡，which意思是 means you are definitely not going to do something你絕對不會去做某件事——a firm, colourful no一種堅決又生動的「不」。It它 is is informal and a bit old-fashioned是口語、有點老派的說法；you hear it from older British speakers more than from young ones比較常從年紀大的英國人口中聽到，年輕人比較少講，often with a laugh常常還帶著笑。

You would not write it in a serious letter.

You would not write it你不會把它寫 in a serious letter進正式的信裡。

The joke inside the phrase is old Cockney rhyming slang: Nelly Duff stood for puff, and puff here meant the breath of life, so 'not on your puff' meant 'not while I still breathe'. Nelly itself is also a woman's name, which is where the Nelly in Nelly Duff comes from.

The joke inside the phrase這個說法裡的笑點 is old Cockney rhyming slang是老式的倫敦腔押韻俚語：Nelly DuffNelly Duff stood for puff代表puff，and而 puff here meant the breath of lifepuff在這裡指的是生命的氣息，so所以 'not on your puff'「not on your puff」 meant 'not while I still breathe'意思是「只要我還有一口氣在」。Nelly itselfNelly這個字本身 is also也是 a woman's name一個女生的名字，which is where the Nelly in Nelly Duff comes from而這也是Nelly Duff裡Nelly的來源。

Students almost never need the word alone; they need the whole phrase.

Students學生 almost never need the word alone幾乎不需要單獨學這個字；they need the whole phrase需要的是整個片語。