This is the 9611th most frequent French word.
déraillé
"Off track" or "derailed."
Here 'déraillé' is used literally to describe a train coming off its tracks.
Le train a déraillé avant d'arriver à la gare.
The train derailed before arriving at the station.
Here 'déraillé' is used figuratively to describe someone's behavior becoming uncontrolled or irrational.
Son comportement a complètement déraillé lors de la réunion.
His behavior completely went off the rails during the meeting.
In this sentence, 'déraillé' is used to express a person losing emotional stability or composure.