IPA: /ˈdɛfənɪŋli/
KK: /ˈdɛfənɪŋli/
In a way that is extremely loud and overwhelming, often causing discomfort or inability to hear anything else.
The music was playing deafeningly at the concert, making it hard to talk to my friends.
Deafeningly → It is formed from "deafen" (from Old English "deafian", meaning to make deaf) and the suffix "-ly" (meaning in a manner). The word "deafeningly" means in a manner that makes one deaf or extremely loud.
Think of the word 'deafen' which means to make someone unable to hear, and the '-ly' indicates the manner in which it happens. So, when something is deafeningly loud, it is so loud that it makes you feel as if you can't hear.