rub
US /rʌb/
UK /rʌb/

1.
1.
2.
症結, 困難
a difficulty or problem, especially one that is hidden or not immediately obvious
:
•
The only rub is that we don't have enough money.
唯一的症結是我們沒有足夠的錢。
•
Here's the rub: we need to finish this by tomorrow.
這裡就是問題所在:我們明天之前必須完成這個。