the elephant in the room

Từ điển Oxford Advanced Learner 8th

the ˌelephant in the ˈroom idiom
a problem or question that everyone knows about but does not mention because it is easier not to discuss it
•The elephant in the room was the money that had to be paid in bribes.
•There's a big elephant in the room and it's gun control.
Main entry: ↑elephant_idiom