WordNet sense 1 (not adhering to ethical or moral principles):

base, dishonorable, immoral, unethical

WordNet sense 2 (contrary to conscience or morality or law):

wrong

WordNet sense 3 (completely lacking nobility in character or quality or purpose):

ignoble

WordNet sense 4 (mean and unworthy and despicable):

shabby

WordNet sense 5 ((used of conduct or character) deserving or bringing disgrace or shame):

disgraceful, ignominious