1640s, "inexplicable," from un- (1) "not" + accountable. Meaning "not liable to be called to account" is recorded from 1640s. Related: Unaccountably; unaccountability; unaccountableness.
权威例句
1. For some unaccountable reason, it struck me as extremely funny.
不知道为什么,我觉得这极其滑稽。
2. He had an unaccountable change of mind.
他莫名其妙地改变了主意。
3. For some unaccountable reason, the letter never arrived.
不知何故,那封信始终未寄到。
4. An insane person is unaccountable for his actions.