IPA: /ˈdɛd.ən.ɪŋ/
KK: /ˈdɛdənɪŋ/
A substance or material that reduces or eliminates sound, often used in construction to make spaces quieter.
The studio was lined with deadening to prevent outside noise from disturbing the recording.
Deadening → It is formed from "dead" (from Old English "dead", meaning no longer alive) and "-ening" (a suffix indicating a process or action). The word "deadening" refers to the process of making something dead or less lively.
Think of the word 'dead' to remember that 'deadening' means the process of making something less lively or inactive.