retarder

noun

1. Something which retards or slows.

   “The substance acted as a retarder to the chemical reaction because it radically changed the pH.”

   “Why is retarder used in dope when the dope is being sprayed in humid conditions? The retarder slows the drying of the dope and keeps it from blushing.”

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.”

   “[...] unlike the latest British yards, Gremberg has only primary retarders, manually operated, a method that the hump operators apparently prefer to electro-pneumatic control because they can grade the braking pressure more accurately by feel.”

3. A refrigerator used to slow down proofing of yeast when making dough.