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blackguard (n.)[blackguard 词源字典]: 1530s, scullion, kitchen knave. Perhaps once an actual military or guard unit; more likely originally a mock-military reference to scullions and kitchen-knaves of noble households, of black-liveried personal guards, and of shoeblacks. By 1736, sense had emerged of "one of the criminal class." Hence the adjectival use (1784), "of low or worthless character."[blackguard etymology, blackguard origin, 英语词源]
flunky (n.): also flunkey, 1782, Scottish dialect, "footman, liveried servant," of uncertain origin, perhaps a diminutive variant of flanker (in reference to servants running alongside coaches; compare footman). Sense of "flatterer, toady" first recorded 1855. "Recent in literature, but prob. much older in colloquial speech" [Century Dictionary].
livery (n.): c. 1300, "household allowance of any kind (food, provisions, clothing) to retainers or servants," from Anglo-French livere (late 13c.), Old French livrée, "allowance, ration, pay," originally "(clothes) delivered by a master to his retinue," from fem. past participle of livrer "to dispense, deliver, hand over," from Latin liberare (see liberate). The sense later was reduced to "servants' rations" and "provender for horses" (mid-15c.). The former led to the meaning "distinctive clothing given to servants" (early 14c.); the latter now is obsolete except in livery stable (1705). Related: Liveried.
flunkey: "A liveried manservant or footman", Mid 18th century (originally Scots): perhaps from flank in the sense 'a person who stands at one's flank'.