unpenetrable

adj

adj

Etymology From un- + penetrable.

impenetrable

'I suppose, inspector,' said Mr Carrados, 'it might seem rather unreasonable of me to ask you to come down here after being in court all day, eh?' 'Well, no, sir,' replied Inspector Beedel with his usual unpenetrable candour; […]1927, Ernest Bramah [pseudonym; Ernest Brammah Smith], Max Carrados Mysteries:

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