The Oxford Thesaurus An A-Z Dictionary of Synonyms - unaccountableadj.

1) unexplained, inexplicable, unexplainable, mysterious, inscrutable, incomprehensible, unintelligible, strange, puzzling, baffling, peculiar, odd, bizarre, unfathomable: I found it unaccountable that anyone would arrive for an appointment four hours early. 2) not answerable, not responsible: How can you have a governmental committee that is unaccountable to anyone? 3 weird, unheard-of, extraordinary, unusual, unorthodox, uncanny: Sophie has unaccountable powers of perception.