IPA: /ˈdɛdənər/
KK: /ˈdɛdənər/
An object or substance that reduces or eliminates sound, vibration, or other effects.
The contractor installed a deadener in the walls to minimize noise from the street.
Deadener → It is formed from "dead" (from Old English "dead", meaning no longer alive) and "-er" (meaning a person or thing that performs a specified action). The word "deadener" refers to something that causes something else to become dead or less lively.
Think of something that makes things 'no longer alive' ('dead') — the '-er' indicates it is a person or thing that performs that action.