Unthinkable; unimaginable—expressing that something is impossible or hard to believe.
こんな結末は考えられない。
This kind of outcome is unimaginable.
彼が犯人だとはとても考えられない。
I can hardly imagine that he is the culprit.
考えられないほどの注文が入り、工場はフル稼働になった。
Orders came in at an unimaginable volume, and the factory had to operate at full capacity.