trail·er / ˈtrālər/ • n. 1. an unpowered vehicle towed by another, in particular: ∎ the rear section of a tractor-trailer. ∎ an open cart. ∎ a platform for transporting a boat. ∎ an unpowered vehicle equipped for living in, typically used during vacations.2. an excerpt or series of excerpts from a movie or program used to advertise it in advance; a preview.3. a thing that trails, esp. a trailing plant.• v. [tr.] 1. advertise (a movie or program) in advance by broadcasting excerpts or details.2. transport (something) by trailer.