Dishonourable describes a person, an act, or a way of behaving that is not morally right — not just clumsy or unkind, but something that brings shame. If conduct is dishonourable, decent people would not respect it: breaking a promise for money, leaving friends in danger to save yourself, cheating in a way that stains your name. It is a heavy, rather formal word. You hear it in speeches, in history, in the army and the law, more than at the dinner table. A child who forgets homework is not dishonourable; a leader who sells out the people might be. British English keeps the u (honour / dishonourable); American English writes dishonorable. Same word, same weight. Though actually, people sometimes throw it around in a fight to sound grand, when they only mean “I don’t like what you did.” The tidy meaning is moral shame, not mere dislike.

不光彩的；可恥的；不名譽的（英式拼法；美式作 dishonorable）