From Longman Dictionary of Contemporary Englishunanswerableun‧an‧swer‧a‧ble /ʌnˈɑːnsərəbəl $ ʌnˈæn-/ adjective 1 ANSWER/RESULTan unanswerable question is one that cannot be answered2 TRUEdefinitely true and therefore impossible to argue against The case (=reasons for doing something) for better public transport is unanswerable.
Examples from the Corpus
unanswerable• But when she arrived on the fine white sand of the cove the question was still there, unanswered and unanswerable.• One last problem remains, but is probably unanswerable.• There were so many questions - all unanswerable.• The path of the law is, as Megarry J. stated, strewn with examples of unanswerable charges which were completely answered.• unanswerable criminal charges• Being unanswerable, it suggests that the terms of the discussion are wrong.• However, it was no use pondering on unanswerable questions.• Nobody, and least of all S. O. Letterman, expects me to come back with answers to unanswerable questions.• This book provides an unanswerable riposte to such nostalgic nonsense. 