impenetrable
adj.impossible to pass through or see through. It can also describe a piece of writing or an idea that is too difficult to understand.
adj.impossible to pass through, enter, or see through; metaphorically describes text or concepts that are impossible to comprehend or interpret.
“The thick forest was impenetrable even with a sharp tool.”
“The lawyer's argument was so full of technical jargon that it remained impenetrable to the average juror.”
“The fortress was protected by impenetrable stone walls and a series of complex moats that had discouraged invaders for centuries.”
Often used both literally for physical barriers and figuratively for intellectual difficulty.
“It is so dense, so impenetrable, so vastly more furnace-like than any previous summer that it makes you angry just walking down the street.”
“In Friday’s speech, delivered to a gathering of law enforcement officials, Trump touted the blockade as impenetrable, and he framed it as a public service for countries that rely on traffic through the strait.”
From Middle English inpenetrabel, inpenetrabyle, from Middle French impenetrable or directly from its etymon, Latin impenetrābilis. By surface analysis, im- + penetrable.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.