IPA: //ʌnˈsaʊndɪd//
KK: /ʌnˈsaʊndɪd/
Not explored or understood; lacking depth or clarity.
The mysteries of the universe remain largely unsounded by scientists.
Unsounded → It is formed from "un-" (meaning not) and "sounded" (from Old English "sundian", meaning to sound or to make a noise). The word "unsounded" means not sounded or not having been made audible.
Think of 'not' ('un-') making something 'silent' or 'inaudible' ('sounded'). This helps you remember that 'unsounded' refers to something that has not been made audible.