Reproach means to express disappointment or disapproval about something someone has done. When your teacher reproaches you for not turning in homework, she's letting you know she expected better from you. When a coach reproaches a player for missing practice, he's showing disappointment in a way that's meant to be corrective rather than cruel.

Reproach carries a particular tone: it's more sorrowful than angry, more disappointed than furious. A parent might reproach a child with a quiet “I thought you knew better than that,” which can feel worse than being yelled at. The word suggests that someone has fallen short of a standard they're capable of meeting.

Reproach can also be a noun. If you act without reproach, you behave in a way no one can criticize. If your conduct is beyond reproach, it's so good that even the harshest critic couldn't find fault with it. A reproachful look is the expression of disappointment someone gives you when you've let them down, the kind that makes you feel genuinely sorry without anyone having to say a word.

The sting of reproach comes from knowing the person criticizing you actually cares about your potential. When someone who believes in you shows disappointment, it matters more than anger from someone who never expected much anyway.