怨言 (yuàn yán): complaint

He works overtime late into the night every day, yet he never utters a single complaint.

The employees have many complaints about the new assessment system, so the manager decided to hold a meeting to listen to everyone's opinions.

My mother took care of my sick grandmother for three whole years, bearing the hardship without complaint; I never once heard her utter a word of resentment.

Despite the harsh working conditions, the volunteers did not complain at all and persisted in teaching in the mountain area.

Rather than complaining behind people's backs, it's better to tell your supervisor your complaints to their face; only then can the problem possibly be solved.