Origin: Latin suffix -ance
Grievance has 4 different meanings across 1 category:
an allegation that something imposes an illegal obligation or denies some legal right or causes injustice
"The union filed a formal grievance alleging that the new policy denied employees their legally protected right to collective bargaining."
a complaint about a (real or imaginary) wrong that causes resentment and is grounds for action
"The union organized a strike to address their grievance regarding unsafe working conditions."
Something which causes grief.
"The unfair treatment by his boss became a source of deep grievance that he couldn't ignore."
In plain English: A grievance is when you feel really upset about something unfair that happened to you.
"The employee filed a formal complaint regarding his unfair dismissal at work."
The word comes from the Old French grievance, which originally meant an irritation or annoyance caused by being bothered. It entered English with this sense of a cause for complaint rather than just general sadness.