Meaning of “impenetrable” - Learner’s Dictionary

impenetrable

adjective uk us /ɪmˈpenɪtrəbl/
CANNOT UNDERSTAND

impossible to understand:

impenetrable jargon
CANNOT SEE/GO THROUGH

impossible to see through or go through:

impenetrable fog

(Definition of “impenetrable” from the Cambridge Learner’s Dictionary © Cambridge University Press)