[intransitive, transitive] to go or to make something/somebody go at a slower speed or be less active Economic growth has slowed a little. The bus slowed to a halt. slow down/up The car slowed down as it approached the junction. The game slowed up little in the second half. You must slow down (= work less hard) or you'll make yourself ill. slow something/somebody down/up The ice on the roads was slowing us down. slow something/somebody We hope to slow the spread of the disease.