I. də̇ˈrāl, (ˈ)dēˈ-, esp before pause or consonant -āəl verb
( -ed/-ing/-s )
Etymology: French dérailler, from dé (from Old French des-, de- de-) + rail, from English — more at rail
transitive verb
1. : to cause (a railroad engine or car) to run off the rails of the track
2. : to throw off course (as a plan or project) : interrupt , divert
new trade barriers could derail British planning — Atlantic
addiction to alcohol, which derailed his career — Val Adams
intransitive verb
: to leave the rails
II. ˈdēˌr-, də̇ˈr-, dēˈr- noun
also de·rail·er də̇ˈrālə(r), dēˈ-
: a device for guiding railway cars or locomotives off the rails at selected points when in danger of collision or other accident