What does "demoralize" mean?

Demoralize: To corrupt or undermine in morals; to destroy or lessen the effect of moral principles on; to render corrupt or untrustworthy in morals, in discipline, in courage, spirit, etc.; to weaken in spirit or efficiency. The demoralizing example of profligate power and prosperous crime. Walsh. The vices of the nobility had demoralized the army. Bancroft.