/ ɪmˈpenɪtrəbl; NAmE / adjective
1.
that cannot be entered, passed through or seen through :
an impenetrable jungle
impenetrable darkness
OPP penetrable
2.
impenetrable (to sb) impossible to understand
SYN incomprehensible :
an impenetrable mystery
Their jargon is impenetrable to an outsider.
► im·pene·tra·bil·ity / ɪmˌpenɪtrəˈbɪləti; NAmE / noun [ U ]
► im·pene·trably / -bli; NAmE / adverb
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WORD ORIGIN
late Middle English : via French from Latin impenetrabilis , from in- not + penetrabilis able to be pierced, from the verb penetrare ; related to penitus inner.