A slower or a retarder is something that reduces speed or activity. It can also be:
Slow motion, an effect by displaying normally recorded footage at a slower speed Slower ball is, in cricket, a slower-than-usual delivery from a fast bowler Zeeman slower, an experimental device that cools atoms "Slower" (Tate McRae song), 2021 "Slower", a 2012 song by Brandy from Two Eleven
See also Slow Slower Than Church Music, a 2002 album by American electronic music group Freescha; A Slower Speed of Light, a 2012 freeware video game developed by MIT Game Lab; Slower Speeds Initiative, a coalition "to raise awareness of the consequences of inappropriate speeds"