From Longman Dictionary of Contemporary Englishovernighto‧ver‧night1 /ˌəʊvəˈnaɪt $ ˌoʊvər-/ ●●○ adverb 1 Dfor or during the night Pam’s staying overnight at my house.2 SUDDENLYsuddenly or surprisingly quickly He became a millionaire overnight.happen/appear/change overnight Reputations are not changed overnight. ► Do not talk about ‘an overnight’ because overnight is never a noun. It is either an adverb or an adjective.
Examples from the Corpus
overnight• Several members of the board became millionaires overnight.• It was a lost opportunity, but you can't change some people overnight.• When radar was directed toward Mercury in the early I960s the situation changed overnight.• We stayed overnight in a motor camp in Picton and continued next day, southwards down the east coast to Kaikoura.• The volunteers fasted overnight, or for six hours after a light breakfast if the study was carried out in the afternoon.• Nothing really worthwhile can be accomplished overnight or without a lot of effort on your part.• I got out of bed, and my back had stiffened up overnight to where I could just barely bend.staying overnight• We were staying overnight at Blackburn bothy, which is set in a small wood with a stream wending through it.• Spend the evening exploring the honeymoon capital of the world, staying overnight at Your Host Motor Inn.happen/appear/change overnight• But they will not change overnight.• He was a patient man: he knew that the attitude of Heads and teachers could not be changed overnight.• Here the dislocation seemed to happen overnight.• When radar was directed toward Mercury in the early I960s the situation changed overnight.• Your footy fortunes can change overnight.• It won't happen overnight, but I can assure you it will one day.• Though the conditions of supply had changed overnight in October 1981, the conditions of demand for mortgage securities had not. overnighto‧ver‧night2 /ˈəʊvənaɪt $ ˈoʊvər-/ ●●○ adjective 1 TIME/HOW LONGhappening during the night or for the night an overnight flight to Chicago overnight accommodation in London2 happening surprisingly quickly The show was an overnight success. his overnight decision to become a vegetarianExamples from the Corpus
overnight• She gave him five minutes to pack an overnight bag under Dexter's supervision and say farewell to his family.• an overnight delivery service• In 1981, it had 26 percent of the overnight market; by 1989, it was down to 12 percent.• After an overnight rain, the sky appeared clear and blue.• The key overnight rate will settle at 0. 45 percent, the same as yesterday, a money market broker said.• Dealer financing rate for overnight sale and repurchase of Treasury securities.• They take eighteen hours all told, including the overnight soaking.From Longman Business Dictionaryovernighto‧ver‧night1 /ˌəʊvəˈnaɪt◂ˌoʊvər-/ adjective [only before a noun]1done in one nightMuch of what is shipped via overnight express delivery is not really needed the next day.2continuing for all or most of the nightan overnight flight3happening last nightLondon stocks ended higher, fueled by overnight gains on Wall Street.4overnight money is lent for one night and must be paid back the next dayCredit was tightened and the cost of overnight money touched 10%.overnight commercial paper —overnight adverbovernightovernight2 verb [transitive] American English TRANSPORTto send something overnightWe were told on Thursday that our check would be overnighted to us on Friday. 