de ‧ rail /ˌdiːˈreɪl, dɪ-/ BrE AmE verb
[ Date: 1800-1900 ; Language: French ; Origin: dérailler , from English rail ]
1 . [intransitive and transitive] if a train derails or something derails it, it goes off the tracks
2 . [transitive] to spoil or interrupt a plan, agreement etc:
a mistake that might derail the negotiations
—derailment noun [uncountable and countable]