Unable to be discovered; hidden perfectly.(adjective)
Not subject to being produced in response to a discovery request.(adjective)
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Use "undiscoverable" in a sentence
"Journalism is about shining a light on subjects masked by shadow, obscured by confusion and hidden by deception to reveal a truth undiscoverable to those without the insight or access to find it."
"Or, it may be the the universe has an undiscoverable rational structure."
"And already the site of the house is undiscoverable, the location of the stone walls may be deduced from the configuration of the landscape, and I am renewing the battle, putting in angora goats to browse away the brush that has overrun Haska's clearing and choked Haska's apple trees to death."