Definitions

1. noun

a person who behaves in a dishonest, unscrupulous, or dishonorable way

“He was accused of being a blackguard for swindling his business partners.”

2. verb

to treat someone with contempt or to behave towards someone in a dishonest or dishonorable way

“He blackguarded his rival in public, calling them a liar.”

3. adjective

dishonorable or unscrupulous in conduct or character

“The blackguard politician was involved in a corruption scandal.”