decelerate v. + Add to list US //dɪˈsɛɫɝˌeɪt// UK //dɪsˈɛləɹˌeɪt// de·cel·er·ate SynonymsAntonymsEtymology Synonyms retardslow Antonyms accelerateOrigin Late 19th c., from de- + (ac)celerate. Compare deaccelerate.