UNSOUNDED

silent, unsounded

(adjective) not made to sound; “the silent ‘h’ at the beginning of ‘honor’”; “in French certain letters are often unsounded”

profound, unfathomed, unplumbed, unsounded

(adjective) situated at or extending to great depth; too deep to have been sounded or plumbed; “the profound depths of the sea”; “the dark unfathomed caves of ocean”-Thomas Gray; “unplumbed depths of the sea”; “remote and unsounded caverns”

Source: WordNet® 3.1

Etymology

Adjective

unsounded (comparative more unsounded, superlative most unsounded)

unfathomed

Source: Wiktionary