From Longman Dictionary of Contemporary Englishtrailertrail‧er /ˈtreɪlə $ -ər/ ●●○ S3 noun [countable] 1 
TTBa vehicle that can be pulled behind another vehicle, used for carrying something heavy► see thesaurus at advertisement2 American EnglishTTR a vehicle that can be pulled behind a car, used for living and sleeping in during a holiday SYN caravan British English3 AMTAMFan advertisement for a new film or television show► see thesaurus at movie
TTBa vehicle that can be pulled behind another vehicle, used for carrying something heavy► see thesaurus at advertisement2 American EnglishTTR a vehicle that can be pulled behind a car, used for living and sleeping in during a holiday SYN caravan British English3 AMTAMFan advertisement for a new film or television show► see thesaurus at movieExamples from the Corpus
trailer• Instead of ploughing into it, however, it struck a tractor and trailer coming from the left.• Time was the people in trailer parks had no doubt that they had a friend in the Oval Office.• The dig was now over, trailers loaded with wreckage headed for home, the diggers contented.• Twin Lakes Fish Camp provides trailer hookups, tent camping sites, and several little cottages.• Nor did he point out that before carrying the sugar beet, the trailer had borne a much more fruity cargo.• Peter Jacobsen probably likes to sit in the front row at movies and be there in time for the trailers.• Go and poison the air in the trailer if you have to.• The movie does have one cinematic innovation: There is a joke in the trailer that is not in the film.From Longman Business Dictionarytrailertrail‧er /ˈtreɪlə-ər/ noun [countable]1MANUFACTURINGan advertisement for a new film, television show etc showing small scenes from itThe trailer was put through rigorous consumer testing.2TRANSPORTa vehicle that can be pulled behind another vehicle, used for carrying materials or goods 