blackguard \BLAG-uhrd\, noun:
1. A rude or unscrupulous person; a scoundrel.
2. A person who uses foul or abusive language.
1. Scurrilous; abusive; low; worthless; vicious; as, "blackguard language."
1. To revile or abuse in scurrilous language.
Blackguard is from black + guard. The term originally referred to the lowest kitchen servants of a court or of a nobleman's household. They had charge of pots and pans and kitchen other utensils, and rode in wagons conveying these during journeys from one residence to another. Being dirtied by this task, they were jocularly called the "black guard."
-- Douglas Murray, Bosie: A Biography of Lord Alfred Douglas