impenetrable
The drink he poured was a stout - an impenetrably black liquid.
The fog was impenetrably dense.
Their opinion is that the country is led by impenetrably smug upstarts who have little experience or wisdom.
SMART Vocabulary: related words and phrases Opaque
cloudy
dense
frosted
mist
misty
murk
murkily
murky
opaque
thick
turbid
turbidity
ultra-dense
You can also find related words, phrases, and synonyms in the topics:
Closing and blocking
Difficult to understand
Impossible and improbable