retarder

noun3

1. •
   Something which retards or slows.

   • The substance acted as a retarder to the chemical reaction because it radically changed the pH.
2. •
   A device for slowing down large trucks, lorries, buses, shunted railway wagons.

   • The hump cabin and its relay room are at the summit of the hump on the right-hand side, and the control tower is on the centre line of the yard between the primary and secondary retarders. — 1959
3. •
   A refrigerator used to slow down proofing of yeast when making dough.