(historical) The lowest servant in a household charged with pots, pans, and other kitchen equipment.
(dated, chiefly of men) An unprincipled, contemptible person; an untrustworthy person.
1830, Thomas Macaulay, Review of Robert Southey's edition of Pilgrim's Progress, in the Edinburgh Review
A man whose manners and sentiments are decidedly below those of his class deserves to be called a blackguard.
2006, Jan Freeman, Blaggards' of the year – Boston Globe
"Arrr, keelhaul the blaggards!" wrote Ty Burr in the Globe last summer, pronouncing sentence on the malefactors who brought us the second "Pirates of the Caribbean" movie.
(archaic) A man who uses foul language in front of a woman (typically a woman of high standing).
verb
(transitive) To revile or abuse in scurrilous language.
(intransitive) To act like a blackguard; to be a scoundrel.