a. Scurrilous; abusive; low; worthless; vicious; as, blackguard language. [ 1913 Webster ]

n. [ Black + guard. ] 1. The scullions and lower menials of a court, or of a nobleman's household, who, in a removal from one residence to another, had charge of the kitchen utensils, and being smutted by them, were jocularly called the “black guard”; also, the servants and hangers-on of an army. [ Obs. ] [ 1913 Webster ]

A lousy slave, that . . . rode with the black guard in the duke's carriage, 'mongst spits and dripping pans. Webster (1612). [ 1913 Webster ]

2. The criminals and vagrants or vagabonds of a town or community, collectively. [ Obs. ] [ 1913 Webster ]

3. A person of stained or low character, esp. one who uses scurrilous language, or treats others with foul abuse; a scoundrel; a rough. [ 1913 Webster ]

A man whose manners and sentiments are decidedly below those of his class deserves to be called a blackguard. Macaulay. [ 1913 Webster ]

4. A vagrant; a bootblack; a gamin. [ Obs. ] [ 1913 Webster ]

v. t. [ imp. & p. p. Blackguarded; p. pr. & vb. n. Blackguarding. ] To revile or abuse in scurrilous language. Southey. [ 1913 Webster ]

n. The conduct or language of a blackguard; ruffianism. [ 1913 Webster ]

adv. & a. In the manner of or resembling a blackguard; abusive; scurrilous; ruffianly. [ 1913 Webster ]