IPA: //ʌnˈɜːrθli//
KK: /ʌnˈɜrθli/
Something that is not from this world, often strange or supernatural in nature.
The music had an unearthly quality that captivated everyone in the room.
Unearthly → It is formed from "un-" (meaning not) and "earthly" (from Old English "eorþlic", meaning of the earth). The word "unearthly" describes something that is not of this earth or beyond earthly existence.
Think of something that is 'not' ('un-') of the earth ('earthly') — that's why unearthly refers to something otherworldly or supernatural.