Part of speech: Adjective (satellite)
situated at or extending to great depth
Example: 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
un – A related word in the same word family.
fathomed – A related word in the same word family.
Tracking word families reveals how metaphors hardened into literal meanings over time.