Insect that infests crossing bitumen? It slows things down

• Any agent that delays or hinders
• Suppressor
• It delays trader, getting involved with worker, perhaps
• Inhibitor
• Tending to delay
• Delaying agent

Wiktionary Word definitions in Wiktionary
a. (context often in combination English) Serving to retard (slow down) the action of something n. (context often in combination English) Something that serves to retard (slow down) the action of something

Wikipedia Word definitions in Wikipedia
Retardant may refer to: Fire retardant Flame retardant