unaccountable

adjective

1 for some unaccountable reason, the horses drawing the cart stopped short:

inexplicable, unexplainable, insoluble, unsolvable, incomprehensible, beyond comprehension, beyond understanding, unfathomable, impenetrable, puzzling, perplexing, baffling, bewildering, mystifying, mysterious, arcane, inscrutable, peculiar, unusual, curious, strange, freak, freakish, unparalleled, queer, odd, bizarre, extraordinary, astonishing, obscure, abstruse, enigmatic;

informal weird, fluky, freaky, spooky;

British, informal rum;

North American, informal off the wall, backasswards;

archaic wildering.

2 the Council is literally unaccountable to anyone:

not responsible, unanswerable, not answerable, not liable;

free, clear, exempt, immune;

out of control, unsupervised.

▷antonyms accountable, liable.

unaccountable Oxford Dictionary of English